Whats Most Important: Weight Variations or Nose Profile

T

The Old Salt

New member
I have a batch of 155g Sierra Palma factory second bullets. (I live close enough to the factory to visit the factory store where they are sold) This batch has a weight variation of 0.8g: 154.8g to 155.5g. The Nose Profiles (NP) vary as much as 0.015". That is the distance from the O-give, measured at bullet dia of 0.297", to the nose of the bullet varies by as much as 0.015". The bullet lengths vary as much as 0.019". Bullet side wall length variations vary with nose profile and total length. So bullet side / bore friction varies as well.

When sorting bullets for loading, which is the most important consideration: weight or nose profile variations? (Remember, the nose is what cuts the air. Different curves cut differently) Everyone understands weight variations. NP variations come into play when loading to consistent C.O.L.s. Even with every consistent C.O.L.s there can be a very significant variation from one round to the next as to how far the bullet moves forward until it engages the rifling. With proper measurements and calcs this can be showed to be as much as 0.020" (especially with Sierra factory seconds).

Just extending the C.O.L.s to the point that the rifling finishes the bullet seating to achieve consistency, isn't always an option. With Palma bullets in my chamber requires a C.O.L. of 2.930" or more to achieve that. This only leaves 0.150" for bullet side in contact with the ID of the case neck.

So once again. Which is the most important: Weight or Nose Profile variations?
Even Sierra's first run bullets will have NP variations of 0.005"!!!
 
These are the 30 caliber rifle bullets here?
https://www.sierrabullets.com/store/product.cfm/sn/2156/308-dia-155-gr-HPBT-PALMA-MatchKing

Okay, there's guys that know this stuff and guys that remember when guys that know this stuff post to the forum.

I'm the latter, I just remember what I read and if it's what I consider a reliable source I pretty much believe it.

That said, I remember folk saying the pointy end imperfections are not very troublesome and not nearly as disturbing as imperfections on the bullets base.

https://thefiringline.com/forums/showthread.php?t=234901

See the above thread post #6. Maybe not intuitively what you'd like to believe but I'm believing that is the way it is.
 
Thanks DaleA. Your post was most interesting and informative read. I have had it all backwards in my view of Nose Profile effects. Their not an issue until the bullet goes sub-sonic and I'll never shoot at those ranges. The base defects impact Drag and Yaw like in an airplane. Makes sence! Since I am currently shooting at 100 yards I'll sort by weight. And stay with that until I start shooting beyond 300 yards. And keep my focus on consistant case prep, trickle tecknique for consistant powder loads and C.O.L.

With that info in hand it's time to load for next Saturday's trip to the range!
 
What is the bullet length from o-give to base ? That is going to be important . Your seater die will contact the bullet somewhere close to the O-give so if the O-give to base measurement is consistent , your distance to the rifling should be as consistent . Having a consistent jump to the lands to me would be more important then O-give to tip distance .
 
Never heard of NP.

But like MG said, measuring from ogive to base is one critical item to look at.

And, at 100 yards, I think you are wasting your time measuring anything to do with the bullets.
 
Starting this thread I learned the bullet base is more important than its nose. HUMMM. Then WHY do RN bullets have such lower BCs than more pointy nose bullets? NP is my own shorthand for Nose Profile. NP is the distance, measured from a consistent diameter on the O-give, to the bullet nose. My 30 cal O-give gauge has a 0.297" ID. Since a .308 bullet engages the rifling at aprox 0.300" a 0.297 ID gauge is close.

Total bullet length - O-give to bullet base = O-give to nose or what I call the Nose Profile.

Having taken the measurements on entire boxes of both SMKs bought at the store, and production seconds for sale at the Sierra factory outlet store. There is a significant difference. First run bullets have a NP variance of 0.005". Factory seconds have a variance of 0.020".

Considering C.O.L., the boxes of Federal Premium Gold Metal Match I have measured had a C.O.L. variance of 0.008".

I do not own a competition bullet setting die. The RCBS & Lee dies I have engage the O-give at bullet dia. of 0.280' & 0.270' respectively. Because of variations in NP, these dies will produce variations in C.O.L., and the O-give to rifling gap. That's just the mechanics of it. So I sort bullets and use a bullet setter that pushes on the very point of the bullet.

The question becomes does the variation in NP have a significant impact on IV and accuracy. Obviously not at shorter ranges, but I'm not going to shoot this rifle at short ranges forever. There are no public and only 2 private ranges int he area longer than 100 yards. The factory test shots from this barrel produced 1/4" groups at 300 yards. Even though I have reloaded for years, I still want to learn everything I can about the fine points of reloading. Even if others have not considered things that are of interest to me, I am interested in their opinions. Thanks to everyone who has shared their knowledge.
 
HUMMM. Then WHY do RN bullets have such lower BCs than more pointy nose bullets?
Click to expand...

Bullet shape and bullet tip shape is very important to specific needs and applications . How ever we are keeping are comments in the context of your specific question . When comparing same bullets from same lot . The few thousandths difference from tip to tip have very little if any impact on external ballistics .

So I sort bullets and use a bullet setter that pushes on the very point of the bullet.
Click to expand...

Not a good idea . Your own measurements show you that .

The RCBS & Lee dies I have engage the O-give at bullet dia. of 0.280' & 0.270' respectively. Because of variations in NP, these dies will produce variations in C.O.L., and the O-give to rifling gap. That's just the mechanics of it
Click to expand...

Your .297 O-give and your .280 &.270 seater will/should have much more consistency then seating by pushing on the very tip of the bullet when it comes to the O-give to lands distance/difference . The O-give to head is the important measurement not COAL . I seat my bullets based on a O-give to head measurement . When doing so my COAL always has a swing of a few thou . But when I measure those same cartridges with my comparator measuring from the O-give to the base/head they are very consistent . That makes the bullet jump to the lands consistent .

Do this , seat 5 bullets using your pushing on the tip method . then seat 5 bullets using your RCBS seating die . Now measure each set of 5 from head of case to O-give . I bet dollars to donuts you will have a more consistent measurement with the RCBS setter die . The measurement that matters most as far as consistency is head to O-give . OAL means almost nothing if you have the ability to measure from head/base to O-give . I use http://www.midwayusa.com/product/23...ad-bullet-comparator-basic-set-with-6-inserts


EDIT :

OK I just went and measured 10 or 41 rounds I loaded yesterday . These are 308 using 175gr SMKs

Head to O-give
1) 2.2075
2) 2.2065
3) 2.2070
4) 2.2075
5) 2.2080
6) 2.2070
7) 2.2080
8) 2.2075
9)2.2075
10) 2.2075

COAL = same cartridges in same order
1) 2.7880
2) 2.7930
3) 2.7990
4) 2.7960
5) 2.7930
6) 2.7960
7) 2.7990
8) 2.7955
9) 2.7875
10) 2.7915

That is .0015 swing from head to O-give and a .0125 swing in COAL . As you can see those rounds will have a pretty consistent jump to the lands but the COAL is all over the place and shows what I mean by OAL means close to nothing if measuring from the O-give .

Those were not seated with a competition seating die but a standard Redding seating die with micrometer that engages the bullet at .270 and my comparator engages the bullet at .300 .

NOTE : Yes I know they are loaded below minimum COAL . It's a long story as to why and not important to the point at hand
 
Last edited:
Metal God,

I think I have not made my point clear, so let me try once more.
1. Sort all bullets using my NP formula.
A. Take a 100 hole bullet board and number every hole.
B. Set up a spread sheet with 4 columns.
i. Bullet Board Hole # (#)
ii. Overall Bullet Length (OBL)
iii. Bullet O-give to Base (BOB)
iv. Bullet O-give to Nose (NP)
C. Take the following measurements on 100 bullets and place them
in the bullet board
i. Bullet overall length (BOL)
ii. Bullet O-give to base (BOB)
iii. Record all measurements in the spread sheet and place each bullet
into the bullet board hole that corresponds to the spread sheet
line (#)
iv. After measuring all 100 bullets have the spread sheet calculate:
OBL - BOB = NP
2. Sort the Spread Sheet so all identical NPs are grouped. You know which
holes in the board they are in because its listed in the spread sheet
3. Select the group of bullets with the NP you wish to load.
4. Load them up and record the Head to O-give & COL for each case.

Here are the results from 20 rounds I just loaded.
Group 1 was loaded with a bullet seater that contact only the nose in my RCBS die.
Group 2 was loaded a Lee bullet seater that makes contact at 0.270” dia.
All bullets were 168 SMKs that were weighed in at 168.1g
The dies were set with bullets 1 & 11 and not adjusted for the 10 rd group.
Group 1
# NP Head to O-give C.O.L. O-give Contact with Rifling
1 0.583” 2.234” 2.815” 2.241” all 10 rds
2 0.584” 2.230” 2.810”
3 0.584” 2.233” 2.814”
4 0.585” 2.226” 2.810”
5 0.585” 2.227’ 2.810”
6 0.585” 2.227” 2.812”
7 0.585” 2.232” 2.812”
8 0.585” 2.232” 2.814”
9 0.585” 2.231” 2.814”
10 0.586” 2.226” 2.811”
Group Specs
Head to O-give ES 0.008”
C.O.L. ES 0.005”
O-give Off Rifling variance 0.011” to 0.015” for an ES of 0.004”
Group 2
# NP Head to O-give C.O.L. O-give contact with rifling
1 0.586” 2.229” 2.817” 2.241” all 10 rds
2 0.587” 2.225” 2.813”
3 0.587” 2.229” 2.817”
4 0.588” 2.229” 2.817”
5 0.588" 2.226” 2.815”
6 0.588” 2.231” 2.815”
7 0.588” 2.225” 2.814”
8 0.588” 2.230” 2.819”
9 0.589” 2.226” 2.814”
10 0.591’ 2.230’ 2.821”
Group Specs
Head to O-give ES 0.006”
C.O.L. ES 0.008”
O-give OFF Rifling variance 0.010” to 0.016” for an ES of 0.006”

If you first sort your bullets by NP:
Bullet length – O-give to bullet base = O-give to Nose or (NP)
Your loaded rounds will enjoy a very consistent set back from the rifling.
Or on the other side you will have a very consistent bullet push back if you
are loading for rifling seating.

So back to my original question.
Which is more important when sorting bullets for loading: weight or NP?
Do you allow a 0.1g or 0.2g variation in weight to get the NP you want?
So you can load with a very consistent O-give to rifling gap...
Or do you let NP vary more in order to hold the weight to 0.1g variation or less?

I don't have the quality of equipment you have. No micrometer dies or comparitor so I have to make do with what I have. The best I could come up with is to sort by Nose Profile. As you can see it does produce results. Less than your 0.0015" in O-give to Head but much better in the C.O.L. (because of the sort) even though it is of little importance, except for mag clearances. My Rem 700 action will run a 2.835" C.O.L. in the mag.
If you are interested in my spread sheet, send me your e-mail address in a PM and I'll send it to you.
 
Last edited:
I have a batch of 155g Sierra Palma factory second bullets.
Click to expand...

Are you trying to get the nth degree of accuracy from FACTORY SECONDS????

Bullets that for one reason or another failed QC?

Why??


Variations in nose profile, hollow points that aren't right, wrinkles in the jacket, mashed or deformed soft points, all these have been tested, and the don't have a major effect on accuracy. Tests were done drilling holes in bullets, (controlled defects). What they found out was that defects in the nose had little or no real effect on accuracy in general use. The same hole in the bullet BASE caused wild inaccuracy.

Old Salt, that is an impressive amount of figures for your group I and group II, loads, but I have to ask, how do they shoot?
 
WOW I had no idea you were doing that kind of detailed work . My short answer to you would be that I would want my O-give to lands distance to be the most consistent . OAL is not important to me in target loads because I load one cartridge at a time and don't use the mag . Yes I'd give up a grain or two in bullet weight to get the jump to the lands consistent .

Not sure how much of the components you have . As I believe 44 AMP may be getting at . Maybe you run some test and see what shoots best seeing how you already have all that detailed data . The next logical step is to do some live fire test and see what works best . I'm interested in what those results would be .

I often come up/across things that I'd like to test but often don't have enough or want to spend the money on the components that would result in a informative test . There's A test I'm going to do some time soon that should answer the question " What's more important Case prep or the bullet used when it comes to accuracy . Now the simple answer is the bullet because to compare a 30 caliber 180gr SMK and a 180gr bullet designed to shoot in a 30-30 whould be silly . No amount of case prep will have that 30-30 bullet shooting like a SMK and vise versa bad case prep is not going to hinder the SMK enough to shoot like a 30-30 bullet . Anyways I'm rambling Here's the thread that sent me on that course http://thefiringline.com/forums/showthread.php?t=562575

I have about 200 cases prepped in many different ways ready to start the test but don't have the bullets to do the test . I was doing some calculations and this test could easily cost over $200 in bullets , powder and primers by the time I'm done including load development and is why It has not been completed yet
 
Last edited:
"Then WHY do RN bullets have such lower BCs than more pointy nose bullets?"

The ballistic coefficient is nothing more than a projectile's ability to overcome air resistance.

A larger frontal surface presents more area for the air to "catch," meaning both that it's harder for the bullet to move through the air, and that it will slow down more rapidly.

It's as if you're dragging your hand through the water. With your palm open, you get a lot of resistance as you move your hand in the water. If you turn your palm so that the side of your hand is moving through the water, it's easier to move your hand because you don't get the same amout of resistance.

The ballistic coefficient can give some indication of accuracy potential, especially with rifle bullets as the move from supersonic to subsonic can throw the bullet off course.
 
How do the shoot? Good question. I am an above average shooter but not compitition level shooter. Same for my loading skills. But I am fascinated by detail. My rifle has a custom barrel chambered to accept standard commercial ammo. I took a case and split it down the neck. I put a bullet in it, chamber it, measure it, to determine when the bullets are sitting on the rifling. Bullets (of the same weight & style) with differentNose Profiles engage the rifling at BOTH different Head to O-give lengths & different case head to O-give lengths.

As for range preformance. I have shot groups as small as .26" @ 100 yrds. I'm told it will do the same at 300 yards. My loading skills keep getting better, but I still have issues with IV ES. I believe the O-give to rifling relationship has an impact on IV ES.

One of my current shooting obsticles is the relationship between the scope parallax adjustment, scope focus adjustment and my progressive bifocals. If i ever solve that mistery i believe my groupings will improve. Aiming through 1 set of cross hairs will be easier than multiples.

I'm just about ready to make the leap from the 100 yard range to the 300 yard. In my area there is only 1. Its private and the first year is pricy. Thats why i have stayed at the conservation ranges until I get the loads & shooting mechanics all worked out.

I plan to shoot this Saturday. We'll see how this all works out. Other than the price savings I can't tell you why I am using the factory seconds. But there is a good reason.
 
Last edited:
I've now been to the range and have some data on the subject. Here is the Cliff Notes version.

Bullets were sorted by weight and NP.
Before measurements were taken, for NP calcs, the HP nose defects were dressed on a stone to provide for more uniform measurements. Some defects could impact measurements as much as 0.007".

All Bullets were Sierra Palma & weighted 155.1G
Loaded & shot in 5 shot groups with specific NPs & O-give to Head specs
O-give to Head specs are unique to each group and based upon the average NP of the Group and how that specific group average bullet chambered.
NP variances within a group were: 0.0000" 0.0005", 0.0010", 0.0015"
There were 6 groups, 3 groups had NP variances of 0.0010"
Win cases with WLR primers, 46.0g H4895,
Loaded w bullets off rifling,
O-give to rifling variances by group 0.0093", 0.0107", 0.0108", 0.0112", 0.0135", & 0.0139"
4 of 6 group IVs in the mid 2900s, the other 2 were upper 2800s.
Group ES: 12. 18, 35, 21, 34, 30
Some groups measured in the 1/2" range or less, others more. (bifocals and shooting skills)
Discussion? Questions?
 

Attachments

Last edited:
My buddy had a batch Berger VLDs (which are supposed to be very accurate) which were almost exactly the same weight but had enough length differences to actually be visible without measuring. They still shot fine though.
 
Group sizes are not on the pdf
Quick measurement with my 6" steel ruler and bifocals does give an idea of the accuracy.
Shooting through progressive bifocals with scope parallax and focus adjustments that produce cross hairs in focus and targets slightly fuzzy. Best I've been able to do.
Can still make out the "X" in the bullseye. A better shooter with better eyes would no doubt produce better results.
87 Deg F, 55% Hum, DP 69, 10 mph cross wind, but fairly steady.
These cases were Win, with WLR primers, shot 3 times previously, twice neck sized, 1 FL resized with neck/shoulder anneal, neck size I.D. 0.3045" to 0.3060". At these COLs there is only 0.150" of straight side of the Sierra Palma's in contact with the case neck I.D.

Group Measurements range 100 yrd
1A, 3/4"
1B, 9/16"
2A, 9/16"
2B, 1/2"
3A, 3/8" (excluding the shot I pulled)
3B, 7/16" (again excluding the shot I pulled)

The best groups I have shot with this barrel were .26" with 175g SMKs. Going to shoot them next time out. Got 30 bullets measured up for loading. Those will shoot from LC cases w WLR primers. Powder, charge wt, and O-give to Head specs are not decided yet.

Barrel was pre-warmed with 20 shots. 10 rds of mil surplus and 10 rds 155g Palma on top of 47.5g LVR. Got IVs up to 3000. Had 3 case extraction issues. Am going to try CFE233 soon as I get some. By the time the last 2 groups were fired the barrel was hot enough to not be comfortable to hold.
 
Last edited:
So to everyone who believes Nose Profile is not important, I hope I made the case that it is. It effects the micro variation in the O-give to rifling gap, which impacts small variations in IV & ES, which impacts vertical dispersion, which impacts accuracy especially at longer ranges. Knowing the NP of your bullets allows you to select those which are nearly identical to load groups that preform consistantly. If I ever get my vision & scope adjustments worked out I hope to shoot 1/4" groups consistantly.
 
With all due respect for all the work you've done and the very tight groups you have shot, I'm afraid we still might have to agree to disagree on nose profile but you've certainly sparked a VERY interesting discussion here. I hope you keep posting.

Good luck.

P.S. If you haven't sold me on this idea please don't lose any sleep over it. I'm not in any way shape or form an expert on the subject, just a guy who shoots once in a while and reads a lot about the topic.
 
You must log in or register to reply here.
Back
Top