Double Grouping on Reloads?

M

MrMajorPain

Inactive
BACKGROUND: I have a 24" heavy fluted stainless steel barrel on my AR15. I'm doing some reloading with Varget and 55 gr FMJ. 2.26 C.O.A.L. and bras O.A.L is 1.75" with various powder weight (26.5, 26.6, 26.7, 26.8, 26.9) and weighed each bullet (between 54.6 &54.7 gr). I've got the RCBS auto powder dispenser so I believe my powder measurements are all accurate. Light factory crimp. Shooting 100 yards. Shooting 5 shot groups. Temperature was a little warmer (by about 5 or so degrees this time than my first set) Wind was left to right about 11 mph first time this time it was right to left about 8 or so.

PROBLEM: When shooting 5 shot groups I am noticing a very consistent pattern of 3 shots grouping (cloverleaf) and then another group about an inch off of 2 (touching). Any thoughts of what this might be? the 26.5 gr and the 26.7 grain shot nearly identical groups and had the two groups vary from left to right. 26.6 shot with the groups varying from up to down.
 
Free float tube?

If a wood stocked bolt action, I would say it is the bedding, but an AR is metal to metal and if the barrel is floated it is not subject to such effects.
 
Another Observation

Another thing I noticed is that I only saw this between 26.6-27.0 gr. and the groupings happened in 2 different shooting sessions. Everything outside of these groups didnt replicate 2 groupings they were just of like normal variations whereas these were "off by groupings"
 
The reason I went with these powder measures is because they performed the best overall grouping from my initial tests (I did high to low on powder and .3 increments in between). So since they had the best grouping that is why I went with that. Do you think it is possible that Varget is just not the best selection for my particular setup?
 
It is curious and does resemble what is expected when heating the barrel causes contact somewhere, so I would inspect and double-check that the floating is being maintained and that no debris or odd item is in the group. If your gun has a horizontal recoil moment it could also be caused by heat changing the bullet barrel time to a different location in the deflection swing of the muzzle. If so, I would expect a chronograph to show a velocity difference between the rounds doing this. It is also possible for the shooter to affect horizontal recoil moments. I always have to add two clicks of right windage when I go from sitting or standing to prone because the butt stock deflects to the right off my shoulder shape when I am in prone. If you shift position at the bench or go from sling to no-sling this can result.
 
A couple of years ago I had a problem that was somewhat similar. Turned out to be the scope. Only way I ever figured it out was that the problem got worse. Boy, I sure ran through some powder and bullets and major frustration with that problem before I read a gun mag article on mysterious grouping problems.

If the groupings were all showing horizontal dispersion, I'd think the problem was 'user error', but that doesn't look to be the problem.

I think I'd try some groups without the crimp. And try some H335 powder if you have it.

So...consider losing the crimp, and then swapping scopes if that didn't help. And tighten the scope mounts/screws.
 
I have zillions of rifles and I help other shooters at the range.

If a rifle is not shooting right, especially two holes over there and then two holes over there, it is more than half the time caused by loose scope base screws.

Never scope ring cap screws or ring to base clamp screws. It is base to receiver screws.

I did a some thinking:

Typically two Weaver scope bases and each base has two 6-48 screws.
Grade 5 bolts are good for 127 ksi in tension
6-48 screws have a 0.12" root [minor diameter]
Area = pi r squared = 3.140(0.120/2)^2 = 0.0112 sq in
Tension = area time stress = .0113 sq in 127 kpsi = 1456 pounds tension per screw
There are 4 screws = 5745 pounds potential clamping force.
The screws are only loaded up typically to 50% of rating = 2873 pounds clamping.

If I look in quickload at the 6.5-06 I just built with a 142 gr Nos Bal tip Long range bullet accelerates from 500 fps to 2000 fps in 0.4 ms.
An 8 pound rifle in recoil reaction would then accelerate in proportion from 1.27 fps to 5.07 fps in 0.4ms
This is a peak acceleration of 9500 ft/sec sec
If a 2 pound scope were attached to a 6 pound barrelled action and stock they would act as an 8 pound single mass.
The mass of the 2 pound scope is = [weight]/[gravity] =[2]/[32 f/ss] = 0.0625 slugs
Force = mass acceleration = [.0625 slugs ][ 9500 ft/sec sec]= 594 pounds of force pushing back on the scope in recoil

The Mausers I just built is made of steel, as are the modified S54 and S46 bases.
Looking up the coefficient of static friction of steel on steel:
https://en.wikipedia.org/wiki/Friction
is 0.74 ~ 0.80 for dry and clean steel
Averaging the two would be 0.77
The static friction force threshold of slipping = [coefficient of friction clean steel][clamping force] = [.77][2873 pounds= 2212 pounds.
Because the static friction 2212 pounds is greater than recoil reaction on the scope mass 594 pounds, the scope should not slip.

But the coefficient of friction for lubricated steel on steel is 0.16
The static friction force threshold of slipping = [coefficient of friction lubricated steel][clamping force] = [.16][2873 pounds= 459 pounds.
Because the static friction 459 pounds is less than the recoil reaction on the scope mass 594 pounds, the scope should slip and the screws should start shaking loose.
 
I thought that it might be the scope but it still is hard to believe that a lose scope ring would consistently be "accurately inaccurate".For instance: I am getting similar results with my "errors" and it seems to follow this specific range of grains with the powder. It just seems that with this specific load it is still making multiple groupings within that specific load. Do you all think that scope rings and/or mounts would be so off to put groupings so that they are touching when they are "off". I guess from my experience when i have a scope mount/ring issues, I have inconsistency in that the scope will not give accurate "misses". My misses are really good if you are looking at how well the group is by itself. There is just something that doesnt seem right to say that the scope would be off because of the recoil but that it would be so consistent and only within those grains.
 
I also think I am going to go with some H335 and see what that gives me as a result as well as losing the crimp. My idea with crimping it was that I really wanted to make sure with the recoil it would not move the bullet. I know a lot of people don't think it will but going back to the post by @Clark I think that the bullet without a crimp would move before a scope mount or ring. Any other thoughts I would GLADLY welcome and I already really appreciate all of the feedback, definitely a lot better knowing I am not the only one who has experienced this.
 
I would also find it hard to believe a rifle could consistently shoot double groups . Then it happened to me .

3xkz.jpg

stga.jpg

sxy9.jpg


Boy, I sure ran through some powder and bullets and major frustration with that problem
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ME TOO !!!!

This is a hardware issue and something is loose . In my case it was loose action screws and is what I thought your issue was going to be . After seeing that this is with an AR I'd say problem with the scope mounting ( blue loc-tite is your friend ) or maybe slightly loose barrel nut allowing the barrel to shift back and forth .
 
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In my case, no way it could have been the scope (new and expensive), but...it was the scope. I went through several powders (Varget, H335, BL(C)-2) and just got ugly groups. They were maybe 1 1/4 inch, but they just seemed random. They were close enough to being decent that I just kept assuming that I hadn't found the right load. Then I was shuffling through debris on my workbench and found some early targets with Varget, and they were pretty good. Hmmm. Groups had gotten consistently worse since then. The only variable I could think of, and what the magazine article had hinted at, was the scope. I swapped it out and bingo, I'm back shooting good groups.

So...I'd take the scope off, then tighten everything that has a screw, nut, or bolt, and try a different scope if you have a suitable one. I know it's a pain, but just get it over with and eliminate that variable. Or, burn some H335 and hope.
 
@metal_god so when you fixed that lose action screw, did that bring the grouping back together?

@603Country I was actually just about to take apart my hunting rifle for end of season cleaning. I think I might try your advice and try that scope on there. Before I do that, I am going to try to tighten the scope mount and rings. You got me thinking so I went and looked back at my groups before. I still had the double grouping but there were definitely closer over all. Perhaps my screws are ever so slightly loose and just getting a little more and more lose.
 
@metal_god so when you fixed that lose action screw, did that bring the grouping back together?
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Yep not another double group in 1200rnds . I did take that opportunity to do some torque test and found the best pounds per square inch each screw worked best at . I then loc-tite them at that torque and It's been GTG ever since .

The funny thing is that the first two pics are sub moa double groups :confused: You'd think a guy would be happy with sub moa groups :D No but really I had seen those come up from time to time but not every group . I was just having problems finding good loads . One day a load would shoot good the next it wouldn't . First I thought it was my shooting ability , then my loading ability , then followed by just confusion . It was after that 3rd pics 10 shot group I knew there was an issue . 10 shots giving two distinct different groups in the same consecutive string is not a random thing . I've always kept detailed notes of all my loads as well as all my targets of load development and any other test I do . It was only after going back and looking through a large amount of my data and targets that I noticed the pattern that kept accruing over a years+ time and a few hundred dollars in components :mad:

I then posted the pics and my problem on this very board and with in a few post was on the right track of solving the problem .
 
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I then posted the pics and my problem on this very board and with in a few post was on the right track of solving the problem
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What is the link to that post? I'd like to read what other people said.

And yes, sub MOA is good but... well you know what it is like when you're reloading. I want all 5 touching :eek:

Thanks again!
 
So what I am saying is that a rifle can shoot great for years, someone rubs oil on it for rust prevention, and it suddenly loses accuracy.
 
@metal_god so you have the savage FCP-K. I have that same rifle and was about to start throwing together some loads for a 168 HPBT Sierra bullet with some Varget and possibly H335. Do you have any suggested loads that you found really good for that match? Also- what is the best load you have worked up on that rifle (powder and bullet combo)?
 
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