Possible short throat on AR10 or maybe Im crazy

[Stevenvalleyky]

I recently purchased my first AR15 and first AR10 after only owning only bolt guns for 30 years. I took the new AR10 out to shoot for the first time recently and Im thinking it might have a short throat. I loaded up some Hornady 168 gr BTHP match with the intent to do some ladder testing with several powders. However, at near starting charges of all 3 powders I was trying, I got what appears to be some cratering of the primers. I also had to morter the gun gently to eject unfired rounds and there appears to be a ring around the bullet. Im thinking that even loading them at 2.805" they may still be too long if the throat was cut short. So far I havent tried running them shorter as Im thinking I already have an issue with pressure, although if the bullet is already jamming into the lands, thats gonna raise the pressure more than shortening them a bit. Am I on the right track here?

 

[243winxb]

The 308 Win has a short Free Bore. Seat bullets deeper? Reduce Powder charge.

 

[Stevenvalleyky]

The 308 Win has a short Free Bore. Seat bullets deeper? Reduce Powder charge.
View attachment 1196470

I load tons of 308 for bolt guns but this is my first for a gas gun. Im currently running them at almost min OAL and what appears to be primer cratering was happening very close to the minumum start charge. Did that look like cratered primers to you or am I imagining it?

 

[243winxb]

cratered primers

We can call it that. But as every one with say, not a good way to read pressure. The firng pin hole can be over size or its just the brand of primer. Some flow sooner then others.

Just watch for a change in the primer, as powder is increase 3/10 th gr at a time.

 

[243winxb]

Factory Hormady ammo is said to be ogive to base at 2.170" ?

https://www.thehighroad.org/index.php?threads/hornady-match-ammo-oal.817988/

 

[JmacD]

No expert, but it could be a gas or timing issie. .

 

[Caplock]

Ejector swipes are a better indicator of pressure.
When your ladder testing and you see those stop and back off the powder. I get nervous with a simi auto and don't hot rod loads. This maybe unfounded.

Find one of your fired cases that a bullet fits in the neck with some resistance. Hand poke it into your chamber. Very gently lower your bolt closed as to not move the bullet. Very carefully eject the bullet not letting it contact anything. The rifling will seat your bullet. Take an average oal length of about 10. Give yourself a 2-3 thousands bullet jump to the rifling.
I will say I've never done this with my ar10 but it works in my bolt guns. I get away with loading to what fits in my mags in my ar10 for over all length.
Another thing to think about is the powder you are using burn range/gas volume work with your simi auto. You didn't say it had any function issues though.

 

[Stevenvalleyky]

Ejector swipes are a better indicator of pressure.
When your ladder testing and you see those stop and back off the powder. I get nervous with a simi auto and don't hot rod loads. This maybe unfounded.

Find one of your fired cases that a bullet fits in the neck with some resistance. Hand poke it into your chamber. Very gently lower your bolt closed as to not move the bullet. Very carefully eject the bullet not letting it contact anything. The rifling will seat your bullet. Take an average oal length of about 10. Give yourself a 2-3 thousands bullet jump to the rifling.
I will say I've never done this with my ar10 but it works in my bolt guns. I get away with loading to what fits in my mags in my ar10 for over all length.
Another thing to think about is the powder you are using burn range/gas volume work with your simi auto. You didn't say it had any function issues though.

I do that with a cut case on my bolt guns to find the distance to the lands, just havent tried it in the AR10. Everything functioned fine although the ejection pattern ranged from 2 to 5 oclock depending on the charge. Rounds were made with CFE223, BLC-2 and IMR4166. 42.0 grains of IMR4166 had a group size under 1/2 inch group at 100 yards but of course that was just 1 five shot group. The other 2 powders had nothing smaller than an inch although with what appeared to be primer cratering, I didnt finish the tests anywhere close to max charges.

 

[Okie_Poke]

If you had to mortar a round to eject it, I’m going to guess you’ve got bullets seated too long. Just because you are under SAAMI max coal doesn’t mean your bullet won’t be jammed into the lands, depending on its shape. I learned a similar lesson with a 6.5 Grendel and 120 grain pro hunters several years ago. As a result, I bought Hornady’s Stoney point tool, a modified case, and a case gauge for every cartridge I reload now.

You need to use some method to figure out at what coal or cbto this bullet is first contacting the rifling in this rifle, and make sure you seat under that. The chamber might be under SAAMI dimensions (that can happen) but it may just be on the min side and your bullet shape is such that it’s touching “early.”

You might also shoot some factory ammo in it and see if it has the same problems. I’d be willing to bet the stuck case and cratered primer are stemming from the same issue, but it’s possible something else is causing the primer issue. You won’t know until you fix or verify the coal issue.

 

[silicosys4]

Drop the bolt on an empty case with a bullet seated only part way. Extract and measure. Then you'll know how your OAL looks for that chamber.

 

[243winxb]

had to morter the gun

TO much crimp may bulge the shoulder, causing this. If crimping?

The COL being to long is a better guess.

 

[Stevenvalleyky]

TO much crimp may bulge the shoulder, causing this. If crimping?

The COL being to long is a better guess.

Yes just a light crimp. Never crimped rifle loads before but started doing it for both gas guns. I imagine Im just contacting the lands. I ALWAYS check the distance to the lands with every bullet in all my bolt guns but was under the impression that I couldnt drop the bolt with a bullet partially in the case to find the lands on gas guns but apparently I can.

 

[DMW1116]

What’s your data source? I’ve had similar issues with my AR10. Hornady bullets get Hornady data. For whatever reason they seem to hit pressure sooner than Sierra or Speer.

CFE 223 is not a powder I like in an AR10. It’s very gassy and caused some timing issues with trying to extract too soon. This resulted in bent rims in my precious few 308 cases at the time. I’ve been reluctant to load an otherwise accurate load with 168 grain Amax bullets and CFE 223. I have an adjustable gas block but the setting for that load is quite a bit off from the other loads I have. I don’t want to mix a load up and use the wrong setting.

 

[bfoosh006]

I recently purchased my first AR15 and first AR10 after only owning only bolt guns for 30 years. I took the new AR10 out to shoot for the first time recently and Im thinking it might have a short throat. I loaded up some Hornady 168 gr BTHP match with the intent to do some ladder testing with several powders. However, at near starting charges of all 3 powders I was trying, I got what appears to be some cratering of the primers. I also had to morter the gun gently to eject unfired rounds and there appears to be a ring around the bullet. Im thinking that even loading them at 2.805" they may still be too long if the throat was cut short. So far I havent tried running them shorter as Im thinking I already have an issue with pressure, although if the bullet is already jamming into the lands, thats gonna raise the pressure more than shortening them a bit. Am I on the right track here?

Is the throat ring all the way around the bullets ogive and uniform ? Then yes you are on track there.

Wilson Combat barrel or Odin Rifleworks by chance ? Or whose brand barrel ?

And Firing pin wise, ( cratered primers ) you will find FP tip size can vary just enough, to matter fit wise.

I would try loading them to 2.800 max...

Oops do the fired cases have any marks on them ? Looking for a poorly cut chamber ( rough )