Twist Rate in AR

[K3]

I have a new varmint rifle w/ 24" bull barrel and 1:8 twist.

Ran some 60gr VMax loads through it that group well in my 1:9 varmint popper. By well, I'm getting 3/4" at 100 in the 1:9, and that's with a clunky 2 stage trigger. The new rifle has a Chip McCormick 3.5# single stage. Smooth as butter.

I got 1-1/2 at 100, and near as I can tell, it's one of two things.

1) I'm not use to the nice trigger.

2) 60gr is marginal in 1:8.

Regarding #2, what experience has anybody had loading 60gr bullets, particularly the VMax for a 1:8 twist .223? I've got some 65gr Gameking loads using H335 that I plan to try next. I also plan to try some 69gr Matchkings as well, but I'm leery of using them on 'yotes. So that's question #2. Anybody have any luck loading up Matchkings for varmint work?

FWIW, my load on the VMax is:

60gr VMax
Win Brass
24.2gr IMR4895
Fed SRP or Win SRP (Haven't had a discernable difference using either)
2.26 OAL

The MV out of my 1:9 is 2600fps (16" bbl). Out of the 1:8, I clocked 2825 on the chrono.

 

[Bartkowski]

I have a 1:7" and it shoots anything above 62gr. very well. 55gr. shoots poorly but should do a little better in a 1:8".

Just try some other loads and if that doesn't work try other bullets.

 

[ar10]

Go to the Armalite or whoever makes the AR clones. The web sites should list them.

 

[BsChoy]

1/8 should run those fine. From what I have read 1/8 and 1/7 twists should run those fine. You might run into problems with lighter more fragile bullets but its not likely with the vmax.

 

[lordgroom]

I have a 1:8 SS heavy barrel 20" and load 55gr FMJ pull downs over 23.0 gr of IMR4895. Accuracy is .60 at 100 yds. I have no experience with 60 gr loads, but it seems my light bullet receives acceptable acccuracy with the 1:8 twist.

 

[K3]

I figured they were probably OK. Just looking for a little confirmation. I'm guessing it was probably the trigger. Surprised me when I fired. Normally that's a good thing, but when you're used to a strong gritty trigger and have learned how to compensate for it, results may very well suffer.

If I remember, I'll post a report when I take it to the range on Saturday and let everyone know how my other loads fared. I'll try the 60gr VMax again too.

Another thing I found was a sticky firing pin. It seemed a tad oversized when I reassembled the bolt group after cleaning. Tried another pin, and it was smooth and moved freely. Could that have affected results?

 

[cracked butt]

Ran some 60gr VMax loads through it that group well in my 1:9 varmint popper. By well, I'm getting 3/4" at 100 in the 1:9, and that's with a clunky 2 stage trigger. The new rifle has a Chip McCormick 3.5# single stage. Smooth as butter.

I got 1-1/2 at 100, and near as I can tell, it's one of two things.

1) I'm not use to the nice trigger.

2) 60gr is marginal in 1:8.

or:
3) The new rifle simply doesn't like that bullet, powder, or combination of the two.

 

[rcmodel]

Whatever it is, it's not the 1/8 twist.

The 60 grain V-Max should shoot quite well in most 1/12 barrels.

rcmodel

 

[K3]

Whatever it is, it's not the 1/8 twist.

The 60 grain V-Max should shoot quite well in most 1/12 barrels.

rcmodel

Yeah, it even says on the box 7-10 twist.

IMR4895 has worked well with several AR loads in various rifles, but I may try some H335 or Win748. I have both on hand.

I've got some 50gr VMax loaded up that shoot extremely well in my 1:9. I may be barking up the wrong tree, but I think I'll give them a go as well. Can't hurt.

 

[K3]

or:
3) The new rifle simply doesn't like that bullet, powder, or combination of the two.

If you're not going to tell me what I want to hear, then don't post...

This is a possibility. Man I sure hope that's not it, because I have 250 rounds already loaded up, and it would be so convenient to have a do-it-all round for both varmint rifles.

Then again, reloading is what it is. It didn't take me long to find the load for my 16" 1:9, so I should find it relatively quickly for this one. .270 was easy. .308 too.

Now, if I can find my .30-06 and .300WM loads, all will be well. Been chasing .300WM for over a year. Starting to think it's the rifle.

To my other question.

Has anybody had good 'on-varmint' results with the 69gr Matchking?

 

[Doug b]

I went to a small mag primer in my bushmaster varminter with H335, Win. brass,and most any good 55 gr. and 60 gr. bullet, broke the rules and collet resized.A mediocre shooter turned into a tack driver instantly.

 

[K3]

I went to a small mag primer in my bushmaster varminter with H335, Win. brass,and most any good 55 gr. and 60 gr. bullet, broke the rules and collet resized.A mediocre shooter turned into a tack driver instantly.

Do you mean neck-sized when you say collet resized?

 

[wcwhitey]

Both my AR's are 1:9, one likes 52 grain Sierra MK's and the other likes the 69's. One Bushmaster and one DPMS. They both shoot 55/62 FMJ reloads about the same, nothing to get excited about but average. Sometimes the rules don't apply it's just what it likes. Bill

 

[MCMXI]

I have a 24" DPMS fluted stainless varmint barrel (upper) with a 1:8 twist on a Bushmaster lower. The first four shots out of the barrel were Black Hills remanufactured 55gr FMJ that a shooter gave me at the range. I was amazed by the accuracy of the Black Hills ammunition given that I bought the barrel to shoot heavier bullets. I reload SMK HPBT 77gr bullets with RL15 powder which work GREAT!!

 

[Doug b]

K3 yep neck sized with a Redding neck die and a Lee collet neck die 100 rnds each.The Redding die had about the same concentricity at the case neck and on the bullet, don't remember the exact number but was comparable to a full length resized round,the Lee collet die held to .0001" runout after resize and after setting the bullet with a dead length seater die.These 100 rnds each were fired 3 times each with 0 FTF.Keeping track of case length with a Stoney Point Head and Shoulders gauge, no change in the base to datum line yet.My point in this test was to see if with the equipment we have today we can reliably reload neck sized ammo for an auto.

 

[Wildfire]

K3.

Hey there.
I agree with most here. Mine is a 1-9 and I shoot the 55s .
24.6 grains of AA2230 and they run at 3071 fps. i get 3/4" groups at 100 when using a scope. Can't see good enough for the irons any more.
Oh. CCI 450 primers. The bullets don't seem to matter much it tosses all 55s about the same.

As for your .300WM. ?? Well I have had some of the same issues with certian rifles. I tune rifles for other people and give them what they want. I have a few that just want deer hunting loads that are accurate. That is what I gave them. These are not very hot loads. But are very accurate.

168 grain Hornady A-Max. 70.0 grains of AA3100 w/CCI 250 primers. .002"
head space. COAL is 3.340"
These loads always run 1/2 to just under 3/4" at 100.
These have taken many deer over the past few years and the guys love em.
As I said they are not max loads, but are accurate.
The rifles were Browning A Bolt, Winchester Police Bolt and Remington 700 Police models. Oh and 1 Interarms.

Good luck .

 

[K3]

QUestion for the experts:

I'm using my RCBS precision mic to try and set me FL die correctly.

The thing is, the fired case measures at 1.4636, and brand new Win or R-P cases are measuring at .004 below that before sizing.

For those familiar with the precision mic, could you give me some insight here?

It seems to me that no sizing is needed. Should I search for cases only .001 or .002 below that? Or are the new cases just right?

 

[Bullet]

For new cases I just make sure the expander ball just goes thru the neck to make sure it is round and then load. After I fire them I then resize to .002 or .003 smaller than a fired case using the mic to make the measurements.

 

[cracked butt]

I'm using my RCBS precision mic to try and set me FL die correctly.

The thing is, the fired case measures at 1.4636, and brand new Win or R-P cases are measuring at .004 below that before sizing

Th shoulder on the brass is going to be pushed forward about .004-005" (or more) when firing new brass. You don't want to resize the brass back to factory specs- just set your sizing die so that you consistantly get 0.002" shoulder setback- ie, if your cases are measuring 1.4636 on your guage (there will probably be 0.001" variation) set your sizing die so that they read 1.4634" after resizing.

 

[K3]

Th shoulder on the brass is going to be pushed forward about .004-005" (or more) when firing new brass. You don't want to resize the brass back to factory specs- just set your sizing die so that you consistantly get 0.002" shoulder setback- ie, if your cases are measuring 1.4636 on your guage (there will probably be 0.001" variation) set your sizing die so that they read 1.4634" after resizing.

If I'm reading my mic right, it only measures to the .001. So, new brass measures at about 1.460. That being the case, then is it safe to say that the new brass is good to go?

If it already measures .004 small, I can't size it to .002 shoulder setback. Or am I missing something? Now, I took some fired brass, and I sized it to .001 to .002 setback, but all of my new brass has at least .003 and in most cases .004.

 

[cracked butt]

Yep, new brass is good to go. Its probably at the minimum spec for a .223 chamber which is roughly what you'd get if you FL sized the brass all the way down with the sizing die set so that the ram 'cams' over.

BTW, I just noticed that I looked at your numbers wrong- set your shoulders back 2 thousanths, not 2 ten thousanths on your fired brass.

 

[snuffy]

The thing is, the fired case measures at 1.4636, and brand new Win or R-P cases are measuring at .004 below that before sizing.

WTH? Your readings are all messed up, if you're using the RCBS mic. You should be getting a measurement of + .001 to +.009 for a fired case. Are you sure you have a precision mic for .223? The left hand part of the mic has | 0 i 1 i 2 and so forth. The barrel or righthand part has the graduations from 0 to 49 on it. The mic is set so that when the the barrel is screwed all the way down on a case, if the case has perfect SAAMI headspace it should read 0-0

With my bushy chamber, firing new factory federal XM-193 American Eagle,(it's LC brass), it ends up at +.007. Setting my FL die to push back the shoulder, I end up at .004 to .005. How you get 1.4636 is beyond me.

 

[K3]

WTH? Your readings are all messed up, if you're using the RCBS mic. You should be getting a measurement of + .001 to +.009 for a fired case. Are you sure you have a precision mic for .223? The left hand part of the mic has | 0 i 1 i 2 and so forth. The barrel or righthand part has the graduations from 0 to 49 on it. The mic is set so that when the the barrel is screwed all the way down on a case, if the case has perfect SAAMI headspace it should read 0-0

With my bushy chamber, firing new factory federal XM-193 American Eagle,(it's LC brass), it ends up at +.007. Setting my FL die to push back the shoulder, I end up at .004 to .005. How you get 1.4636 is beyond me.

No, my readings are correct. They are below the min by .004 for unfired cases, and the fired cases out of the rifle reads at or .001 above the min.

1.4636 may or may not be the min. I didn't type this at the reloading bench. I have the specs with the mic, and I assure you that I am reading it correctly. This isn't my first rodeo using measuring devices. If I can read vernier calipers with no problem, a little mic like this is not a big deal.

 

[MCMXI]

If I'm reading my mic right, it only measures to the .001. So, new brass measures at about 1.460. That being the case, then is it safe to say that the new brass is good to go?

If it already measures .004 small, I can't size it to .002 shoulder setback. Or am I missing something? Now, I took some fired brass, and I sized it to .001 to .002 setback, but all of my new brass has at least .003 and in most cases .004.

K3, I don't think you're missing anything. If the shoulders on your new cases measure SAAMI - 0.004 inches then there's not much you can do except fire form them to your chamber dimensions which sounds like it's SAAMI + 0.001 inches. Of all the cases that you've measured, what's the largest increase in headspacing that you've seen? For some of my bigger calibers, it may take three or four firings (with neck sizing only) before the shoulder stops creeping forward.

 

[K3]

K3, I don't think you're missing anything. If the shoulders on your new cases measure SAAMI - 0.004 inches then there's not much you can do except fire form them to your chamber dimensions which sounds like it's SAAMI + 0.001 inches. Of all the cases that you've measured, what's the largest increase in headspacing that you've seen? For some of my bigger calibers, it may take three or four firings (with neck sizing only) before the shoulder stops creeping forward.

I've got one AR that takes new brass and pushes it to SAAMI +.006 or .007. This new rifle does in fact do what you say and go to SAAMI +.001 (sometimes SAAMI + electron ), IOW, a very tight headspace. (I think that's what I mean to say).

Now, do you think the cases being SAAMI -.004 is affecting my accuracy given my chamber dimensions? This bugged me all night. I kept going back and forth between brass dims and 'do I have the right component combo?'.

I'm going to try some loads using Varget, RL15, H335, and Win 748. I also intend to adjust the charge weight on my IMR4895 and see what effects that has. Like folks have mentioned, every rifle is different. I guess I was unrealistic hoping that an accurate load that I developed doesn't do the same in a new rifle.