Semi auto advice needed

[CNY Yote Hunter]

To start I have been reloading for close to 20 years or just over that. That being said I came across something I haven't seen before today. Well out with a friend sighting in a new thermal on his rifle I found my load I have been using in my bolt gun does not fully extract on his semi auto. Rifle is a 204, not sure the model or action and I apologize cause I know it's kind of needed info to possibly answer this. My load is a 32 grain vmax, brass is nosler- new, federal 205 primers and pushing 4000 fps out of my 26" savage barrel. His barrel is only 18" so obviously speed changes quite a bit but when he shot my load he hit the bullseye at 100 and drop out to 500 was the same as the factory loaded superformance. With the factory loads his gun fully cycles but with mine it does not… what am I missing? Do I need a crimp for more pressure?
I do not own any semi autos and I don't load for anyone generally but with ammo being so non existent we wanted to see how mine shot in his just in case type of scenario…. Who has answers lol and happy holidays from NY!!!!

 

[ARlife4me]

So is it in an AR platform. Production gun or a built or an upper change?

 

[CNY Yote Hunter]

So is it in an AR platform. Production gun or a built or an upper change?

It is an AR yes and non production, built it himself. I can grab details from him on the gun tomorrow and post as I'm sure it might help….

 

[ARlife4me]

It is an AR yes and non production, built it himself. I can grab details from him on the gun tomorrow and post as I'm sure it might help….

204 ruger?

 

[ARlife4me]

18" rifle length or intermediate gas length? Does he use the lower for a different upper cartridge? Is there an adjustable gas block? Carbine or rifle stock? If a non-adjustable gb is used you might need to reduce the buffer weight or spring weight. Does it try to double feed or just doesn't fully cycle after being fired? Tons more questions!

 

[CNY Yote Hunter]

18" rifle length or intermediate gas length? Does he use the lower for a different upper cartridge? Is there an adjustable gas block? Carbine or rifle stock? If a non-adjustable gb is used you might need to reduce the buffer weight or spring weight. Does it try to double feed or just doesn't fully cycle after being fired? Tons more questions!

Thanks for the response and questions. It is a 204. He has never used the lower with another upper cartridge. It's always stayed the same. No clue on gas block, I will ask him tomorrow, it does not try to double feed, it will not fully cycle. I will ask him tomorrow on the questions I don't have the answer to and let you know

 

[ARlife4me]

Thanks for the response and questions. It is a 204. He has never used the lower with another upper cartridge. It's always stayed the same. No clue on gas block, I will ask him tomorrow, it does not try to double feed, it will not fully cycle. I will ask him tomorrow on the questions I don't have the answer to and let you know

Also I need mag info. Mag brand, number of rounds, 20 round with a limit of 10 and so forth.

 

[CNY Yote Hunter]

Also I need mag info. Mag brand, number of rounds, 20 round with a limit of 10 and so forth.

Copy that, I will send it your way.

 

[ARlife4me]

Copy that, I will send it your way.

pm has been sent also

 

[Zen Archery]

Sounds like my old Varget load which has more than enough pressure to cycle an AR, maybe too much gas for his AR.

I'd try 2 things
A). Develop a load 1 and 2gr under and see if it cycles. Hot loads can seal a case to the throat causing FTC (Fail to cycle) issues. [Trust me as one whose shot a 17cal out to 5060 FPS].

B). Break down a factory load bullet pre-shot and post shot and grab all the measurements and compare it to your load development. Paying really close attention to case and shoulder length. Small caliber AR's running hot loads (refer to above) can be finicky with case length and shoulder jump.
Grab post shot case info to see how much jump factory load is allowing for case and shoulder length.
Reverse engineer case specs and start from there.

if factory load is cycling my spidy senses is guessing your case length is touching or slightly feeding into the throat. When launching a tiny bullet with that much heat it's temporarily sealing the case to the throat causing fail to cycle.

Good luck, keep us posted.

 

[CNY Yote Hunter]

Sounds like my old Varget load which has more than enough pressure to cycle an AR, maybe too much gas for his AR.

I'd try 2 things
A). Develop a load 1 and 2gr under and see if it cycles. Hot loads can seal a case to the throat causing FTC (Fail to cycle) issues. [Trust me as one whose shot a 17cal out to 5060 FPS].

B). Break down a factory load bullet pre-shot and post shot and grab all the measurements and compare it to your load development. Paying really close attention to case and shoulder length. Small caliber AR's running hot loads (refer to above) can be finicky with case length and shoulder jump.
Grab post shot case info to see how much jump factory load is allowing for case and shoulder length.
Reverse engineer case specs and start from there.

if factory load is cycling my spidy senses is guessing your case length is touching or slightly feeding into the throat. When launching a tiny bullet with that much heat it's temporarily sealing the case to the throat causing fail to cycle.

Good luck, keep us posted.

This makes really good sense since it's new brass so never been fire formed and I've heard the nosler brass for the 204 is terrible but it's all I could get my hands on so it's what I have. I have the spent case from that and I'm curious to take measurements now. Also could be the difference in brass as his factory load is Hornady so Hornady brass!!! Thank you for the response, this makes sense and I will let you know what I find with it.

 

[Fiftydriver]

this can be caused by a couple things, could be over pressured which causes the bolt to unlock and start extracting the case before chamber pressures drop enough for the case walls to release the chamber walls. This can cause the extractor to slip over the rim and leave it in the chamber. If this is happening you will usually see rim damage. Sometimes using a slower burning powder can help this.

it could also be underpressures which means the dwell time is to short and Not enough pressure is being applied to the bolt to make it fully more to the rear. Sometimes a faster burning powder can help this.

However, likely the best fix would be to use an adjustable gas block so that you can tune the rifle specifically to the load being used for best function. If its currently over gassed, choke down the gas block valve to slow down the bolt unlock. If its under gassed, open the gas valve more to allow just enough bolt travel so that the bolt will consistently lock open after the last round is fired out of the mag.

 

[CNY Yote Hunter]

So to update all that have responded we have our answers…. 1, it has an adjustable gas block on it and adjusting it fixed the issue for sure. On top of that though I measured the cases out of that and compared them to the cases out of my bolt gun and am amazed at the difference in lengths of the spent cases. Consistently .015 longer on the AR fired brass than the bolt gun fired brass with the 6 pieces we measured. Neck diameter was also .010- .005 more on the AR fired brass vs the bolt gun and had one primer out of the 6 in the AR start to come out of the brass. So now my next question, the overpressure would be a clear cause of the primer issue, I'm assuming the gas block would have also been the cause of that too? So why would someone put an adjustable gas block on an AR? Is the same gas block usable for different calibers and how would one adjust it to specification and is there a pressure range specific to each caliber? Trying to learn here guys so don't judge me on this lol, I'm a bolt gun guy and have never owned or built an AR but the time is near I feel lol!!!

 

[Turpentine21]

You use an adjustable gas block to regulate the speed of your bolt carrier. If the carrier starts coming back to early before your fired brass shrinks you can get case head separation. If it's over gassed the extra bolt speed can also be tough on the gun. An Adjustable block allows you to tune bolt speed. And get your ejection angle correct. You can also tune with buffer weight and spring stiffness.
There is likely a large dwell time difference between his gun and yours because of barrel length and gas system length. One may also be over gassed or under gassed due to port size. Even the difference in chamber sizes will make a difference.