Weird Performance.....

W

Wildernesshunter

New member
I wanted to start another thread, because I think this is a completely different topic, off of the other thread on the 7.62x39.

Yesterday, I loaded eight rounds of the following: 7.62x39, A2200 Powder, Speer 150gr SP.....all have identical bullet seat. I am shooting at a 200 yd target.

26gr.....27gr.....28gr.....29gr

Here's were it gets weird.....

I shoot the first four rounds of 26gr and I get a darn good group of 1.9". Velocity averaged 1,980 fps.

Then I shoot four rounds of 27gr and I get a 2.5" group, but the group is 2" lower than the 26gr group. Velocity was 2,095 fps.

Then I shoot four rounds of 28gr and I get a 4" group, but the group is 4" lower and 2" to the left than the 26gr group. Velocity was 2,190 fps.

I finally shoot the 29gr rounds and I get an 8" group that is 8" to the left of the 26gr group. Velocity was 2,275 fps.


I was so puzzled and confused, mainly in that as velocity increased, bullets fell more.

On the drive home from the range, it occurred to me that maybe....just maybe....

....my bullets are fairly stable at 2,000 fps with 26gr of A2200....but as the velocity climbs, the bullets are destabilizing more and more as muzzle velocity increases, hence loosing velocity the more they are destabilized. 29gr of powder and nearly 2,300fps are creating the poorest performing load.

Maybe this is an issue with my gun and the twist rate, etc..... but this is what I am seeing and this is my guess.

I would love any additional input.
 
I think what you might be experiencing is the effect of barrel whip when you are shooting the same bullet at different speeds through the barrel.
 
Who knows? It is possible the bullet is destabilizing as it leaves the muzzle meaning the pressure can not wait for the bullet to get out of the way; and then there is a chance you need to change the bullet like reduce the powder and increase the weight of the bullet.

I have taken 120 rounds to the range loaded in 12 different ways with different powders, cases, bullets when testing a new build. I have had groups to move but never spread. All of this in an effort to find what the rifle liked.

F. Guffey
 
I don't think its particularly about twist.

Do you have dovetails cut across the barrel?

Could be a bedding issue.Tight spot in the barrel channel,guard screw interference...any bedding problem could be aggravated as charge goes up.

Load density? Are upper charges compressed?

Sometimes its just a mystery."I do not know why my rifle does not like.......but when I changed (bullet,powder,primer,etc) it shot a lot better"

No disrespect,but groups opening up as zero shifts can be about recoil/noise anticipation.Closing your eyes.I know,the 7.62x39 has little recoil.

Try REALLY concentrating on seeing the reticle on the target ,and calling the shot .What did the reticle look like on the target at recoil?
If you cannot capture that image,your eyes are closed.You might have a friend slip a dummy round in your magazine.Dropping on a dummy round can be revealing.
 
This is something you see not uncommonly with rifle length barrels but not with shorter handgun length barrels. It usually is due to recoil moments and pressure distortion of the barrel bending the muzzle through a whipping motion and getting the bullet out at an unfavorable portion of the that motion. Ideally you want the bullet exit to coincide with a relatively slow changing portion of the move as occurs near its extremes. As Mr. Guffey suggests, changing bullets to a heavier one may let you put more energy in the bullet without shortening the barrel time to a point in that movement that is less favorable than your light load produced. However, as he also suggests, it could be other things. The recoil may simply grow enough with that higher load to start forcing barrel-to-stock contact or some other issue that throws the shot off. Any whipping associated with recoil and pressure will become greater as the pressure increases.

Here's a page with an animated FEA analysis of a rifle with a barrel tuner getting this sort of muzzle deflection exaggerated 500%, though the tuner slows it some. Without the tuner, the barrel whips faster and could let your bullet out while it is lower and rising fast or even rotating over to the side (see other harmonic motions when you scroll down).
 
Here are some other factors that may lead to helping you guys....help me....

The barrel on this Howa is a .310 and these bullets are .311.

As you know, the 7.62x39 was designed for 123gr bullets. These Speer bullets are 150gr.

The gun is the light weight version of the 1500 Mini Action and the barrel is a really thin......pencil barrel. It is 20" long.

The stock is really stiff and solid, the best synthetic I have ever owned or shot and the barrel is free-floated.

This gun shoots a solid, legitimate 0.5 MOA with Winchester Accuracy Rounds in a 123gr fmj. It is crazy accurate.

I simply wanted to be able to run a better hunting bullet through it, which has proven to be incredibly elusive in the accuracy department.
 
The thinner the barrel, the more it whips. So, same answer. Your bullet just isn't exiting with a barrel time that synchronizes to the whipping. You could fire an Auddette ladder and see this if you have longer ranges available. Or you can try Dan Newberry's OCW charge weight identification system. It works at 100 yards.

You may find that the light barrel floating is not best. O'Connor bedding may do better. This is where you weight the front of the stock down with 15-20 lbs while wedging paper match sticks between the barrel and stock, then releasing the load on the stock. You try these paper wedges in different positions until you find an accuracy sweet spot for the bullet you want to use. They can be fixed permanently to the stock with epoxy later.

OConner%20Bedding%20B_zpsk4sgtzys.gif


This place makes a system that does the same thing but is tunable for different bullets.
 
I guess the pursuit of great accuracy, will come with its challenges. Thank you so much for the information. Suppose I need to start playing around with shimming the barrel.

I am honestly wondering if I purchased the wrong gun in the first place, in buying this little guy with a #1 barrel. I know it would add a pound of weight to the gun, but I am now wishing I have the heavy, #6 barrel.

I have sent a message to Howa USA with all the info I could provide, asking for their feedback, suggestions and help. I will share what they share with me.




.....
 
Old Bill Dibble said:
That and possibly some barrel heating as well.
Click to expand...


You didn't say what your time between shots and groups was. Was the barrel heating up a factor.

Whenever I'm testing loads like that I'll hang a target for each load and label them. I then shoot 1 round of the first load at the first target, then one of the second load at the second target and keep working my way around. That way barrel heating/fouling is spread out amongst the various loads rather than getting worse as you try different loads.

I don't know if you're new to this but I can only echo what others have said about patience with different loads. I was fairly convinced my daughters gun was a 2 MOA gun, at best. A friend suggested I try a particular load and even gave me 20 bullets to try (I had been hesitant to try these bullets because they are a little expensive). I messed around with a couple of powder combinations and ended up with a load that I can consistently get 5 rounds touching. More importantly, so can my daughter.

The biggest thing I learned in the process is that guns are mysterious creatures with a ton of variables and you can only control so many of them.

If this was my load results I would probably load up a bunch of rounds around the 26 grain load (25.5, 25.8, 26.1, 26.4, or something like that) and shoot those. Obviously your gun "likes" something around 26 grains, I would drill down a little and try to find the specific charge weight it likes the most. I've seen measurable differences in a .1 difference in powder weight.

Once I found the right charge weight, then I would start monkeying with seating depth.
 
Four rounds.....wait to cool......four rounds.....wait to cool.....etc....

This is generally how I shoot all my guns and usually take three to four to the range, rotating them for shooting.

Does my gun like 26gr rounds.....or does my gun like a lower velocity with the 150gr bullet? I don't think it is as simple as finding a powder and amount first. With only a 20" barrel, I do need a quick burning powder. Based on a lot of positive experience with A1680.....that's what I thought I would use, but upon further research, A2200 seemed even better. I will agree with you, that I should try 3-4 other powders and bullets.



I did get a reply back from the Howa brain-trust. They were very helpful and very prompt.

Their gun guru was up-front in stating that they developed and built the 1500 Mini Action in the 7.62x39 for the 123 gr bullet and they believe my attempts with a 150 gr, .311 bullet were destined to fail from the beginning. They asked me to buy a box of Hornady 123gr, off the shelf ammo and give it a go.

I'm ok with this response and understand why Howa would do this. After all, every gun off the shelf is purpose built for a specific load, be it barrel twist or length of barrel or weight of barrel, etc. My savage .223 will not accurately shoot 80 gr match bullets. It will drive tacks with 69 gr bullets.

If I can get some Hornady SST 123's shooting straight as a string, I will be a happy camper.
 
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Give that a try. Also, put up four targets for your four shots; a shot 1 target, a shot 2 target, a shot 3 target, and a shot 4 target. Run your several groups always putting the first shot on the shot 1 target, the second shot on the shot 2 target, etc. This way, if there is a consistent thermally related behavior, the groups on these targets should be tighter than the groups of four in a row, and you will be able to plot the group centers and see how much hold-off you need for each successive shot as the gun heats, and in what direction.

Did you follow the Howa break-in method with this rifle? Scroll half way down this FAQ to find it.
 
Wildernesshunter said:
Does my gun like 26gr rounds.....or does my gun like a lower velocity with the 150gr bullet?
Click to expand...


I think it's related either way. I went back and looked at the velocity and pounds of energy and realized the lower velocity loads probably aren't giving you the down range energy your after.

I still think you could get the 150's to shoot (you shot an MOA group at 200 yards) and with some further tweaking in powder and seating depth I think you could get something better but realize now its probably not worth the effort because of velocity.

Either way I'm enjoying your review of the Howa rifle. I'm looking for a factory 6.5 Creedmoor and Howa was one of the brands I've looked at but don't know much about.
 
Hey....I haven't dropped this project, just got distracted with the Holidays and another gun project (Rem 700 7mag bench-rest).

Anyway, I have 120 pieces of brass that I wanted to anneal....cause I have never done that. Annealing is done and now I just need to resize, trim and reload and then go to the range.

Since I started with this little gun, I needed to swap scopes, so it now sports a Bushnell Banner 2-7x32. I sighted it in this past weekend with Wolf ammo.

Anyway.....reloads with the Hornady bullets and Accuracy 2200 is coming soon.
 
"I simply wanted to be able to run a better hunting bullet through it,"

I simply don't see that using a 150 grain bullet makes for a better hunting load.
The 7.62x39 is already "velocity challenged" so adding bullet weight just makes it worse. A .310 bore is a compromise and being "neither fish nor fowl" makes bullet choices more elusive.

"This gun shoots a solid, legitimate 0.5 MOA with Winchester Accuracy Rounds in a 123gr fmj. It is crazy accurate."

If this is true, I'd make every effort to match bullet velocity, diameter, length, weight, and shape to this load.
FWIW, I've found that some lots of Remington 125 (described as "308") bullets miked @ .3095" and shot quite well in a .310" bore. They also performed fairly well on deer under 150 yards.
 
POI walking away in one direction as groups get bigger. That sounds like something coming loose. The rifle probably doesn't have a muzzle brake, so maybe something scope-related.
Don't see how it could be a stability or twist rate issue. Could look it up on a stability calculator, but that's not a long bullet.
Wolf sells 154 gr hunting ammo.
 
The original reason I wanted to pursue the 150gr bullet was the ballistic coefficient is much higher than the 123gr. At 300 yards the 150gr has much more energy and superior ballistics.

But as stated in a post above, the Howa engeneers state plainly the gun is designed to the 123gr bullet.

Nufff...said.... 123gr bullets are being loaded next.


"I simply wanted to be able to run a better hunting bullet through it,"

I simply don't see that using a 150 grain bullet makes for a better hunting load.
The 7.62x39 is already "velocity challenged" so adding bullet weight just makes it worse. A .310 bore is a compromise and being "neither fish nor fowl" makes bullet choices more elusive.

"This gun shoots a solid, legitimate 0.5 MOA with Winchester Accuracy Rounds in a 123gr fmj. It is crazy accurate."

If this is true, I'd make every effort to match bullet velocity, diameter, length, weight, and shape to this load.
FWIW, I've found that some lots of Remington 125 (described as "308") bullets miked @ .3095" and shot quite well in a .310" bore. They also performed fairly well on deer under 150 yards.
 
I purchased a rifle for parts; the cost was $120.00 + shipping. With the help of my friends:rolleyes: the rifle was designated 'the ugliest'. For me accuracy is first and then 'ugly' can be decided later. BUT: on the outside chance the ugly rifle was built by someone that knew what they were doing I loaded 12 different loads with 12 different cases (new, once fired, formed, commercial and military surplus), different bullets and powders. I used different cases for sorting after tumbling.

I took the rifle to the firing range with 120 rounds to test the rifle. Out of the 12 different loads I did not have a group open up and there were no flyers. Rather than build another M1917 rifle I applied the leaver policy; I 'lefter' like I founder. Each of the 12 groups could be covered with a quarter. That would be 10 holes in each group.

The rifle did not come with load instructions, the rifle reminded me of the days when racers raced for titles. I considered the builder of my ugly rifle put everthing he knew about accuracy into the rifle without spending 'a lot' of money.

F. Guffey
 
"At 300 yards the 150gr has much more energy and superior ballistics."

Just my opinion: 7.62x39 is NOT a 300 yard hunting round regardless of bullet weight. Hitting a game animal and killing a game animal cleanly have different requirements.
 
Yeah, fair enough. Even my own rule of thumb is for a load to have at least a 1,000 ftlbs of energy at a given yardage for deer. My handloads will have have over 1,000 ftlbs at 250 yards, but not 300.

Still, my Howa is a great little gun, one I love to shoot and my wife's favorite for a deer rifle.

The only deer I have killed with it was lasered at 263 yards, a low chest hit in the heart and it was dead only 25 yards from impact.
 
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