375 Raptor

[Speedluvn]

I’ve been reloading for about 4 years or so. I reload every caliber that I shoot. I rarely buy loaded ammo. With that said, I just completed a 375 Raptor build on an AR10 platform.

I loaded about 20 rounds and shot them this weekend. I experienced some blown primers and other high pressure signs. I came home and checked my data. I purchased a case length guage from an eBay seller.

My question is the cartridge case in the guage should be flesh, correct? I’m seeking another set of eyes on this issue.

 

[DavidA]

Here you go.

So case gauges are great for basically determining if your shoulder is set properly on your sizing die. I the ultimate reminder instance he did not seat the shoulders back far enough and he had problems getting his rounds into battery. To much shoulder push back and your letting the case expand to much all at once and you risk case head separation. When you’re getting close to that you’ll start seeing a line in the brass about a 1/4” past the case heads. This is not good.

But every barrel has a chamber which may be slightly a couple of thousands different from each other. So this is why many reloaded simply take once fired brass and place s comparator on the shoulder. Then when the set up their full length sizing die so that just bumps the shoulder back a couple of thousands.

Now will say a shoulder bring push back to far cause blown primers. Not really the case as primers blowing can be one of two reasons. Either your primer pockets are loose, your primers are not seating properly, or the case is over pressure.

For AR type platforms another thing that can happen is if the gun is over gassed. When this occurs the dwell time ( time bullet passes gas port to the exit of bullet from barrel) and the level of pressure at the gas port are too high. So the round starts to begin being extracted while there is still a lot of pressure on the case in the chamber. You can help mitigate this by using a heavier buffer, and an adjustable gas block.

In gas gun when you’re loading heavy bullets with powders that are slow burning, pressure within the barrel is very high for a longer period of dwell time. I had a 20” LR308 with a rifle length gas block that when I started running heavier bullets with slower powders it just beat the hell out of the brass and yes I blew some primers. Solution was a combination heavier buffer (KAK 8.6oz rifle buffer) and an adjustable gas block. It just slows the whole gas system down.

Not aware of all your loading and other systems associated with your loading but these are just a summary of what my experience has been. I hope this helps, but bottom line my guess is either a gas system dwell issue created by longer dwell times with gas pressure still on bolt, or you are simply loading it to hot.


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[smdub]

I'm interested in what you find out here as I've been intrigued by the Raptor rounds for a while.

 

[Speedluvn]

The first thing that I noticed after the issue appeared was that the case gauge appears to be too short. My cases were measuring 1.821.
The diagram attached above indicates that it should be 1.865.
I purchased the case gauge from an eBay seller. I’ve had communication with the seller and will be returning the gauge for a replacement.
In my limited experience, I’m suspecting that my bullets were seated too deep.
My data came from the 375 Raptor site that appears to completely down now.
I was shooting 270 grain Speer at 2.700.
Thoughts?

 

[DavidA]

Take a fire case and before you full size it, put a comparator on the shoulder and find out what the dimension base to the shoulpder at comparator. Set the full length sizing die so that it bumps bak the shoulder .002 " or 2 thousanths. Next measurte your chamber. All chanmbers are not the same. Measure the cartridtges Cartridge Over All Length base to tip with the bullet kissing the lands. Change the COAL so the bullet is back .030" to .040" from the lands (30-40 thousands back) . then back your load off 10% and run a ladder 2 graiin increments to max and look for pressure at each case firting.
Check primer pockets of brass , in case it was over presured significantly.

 

[85MikeTPI]

I’ve been reloading for about 4 years or so. I reload every caliber that I shoot. I rarely buy loaded ammo. With that said, I just completed a 375 Raptor build on an AR10 platform.

I loaded about 20 rounds and shot them this weekend. I experienced some blown primers and other high pressure signs.

Do you full-length size your brass? I know many folks with uncommon calibers, try to extend brass life by neck-sizing, but the AR platform will stick rounds and show pressure signs when the brass won't smoothly eject.

 

[Speedluvn]

Take a fire case and before you full size it, put a comparator on the shoulder and find out what the dimension base to the shoulpder at comparator. Set the full length sizing die so that it bumps bak the shoulder .002 " or 2 thousanths. Next measurte your chamber. All chanmbers are not the same. Measure the cartridtges Cartridge Over All Length base to tip with the bullet kissing the lands. Change the COAL so the bullet is back .030" to .040" from the lands (30-40 thousands back) . then back your load off 10% and run a ladder 2 graiin increments to max and look for pressure at each case firting.
Check primer pockets of brass , in case it was over presured significantly.

i loaded a few rounds that way and that’s how I realized there were issues. I was also breaking in the barrel.

Do you full-length size your brass? I know many folks with uncommon calibers, try to extend brass life by neck-sizing, but the AR platform will stick rounds and show pressure signs when the brass won't smoothly eject.

Yes. I full-length resize my rifle calibers.
The brass was 308 mixed headstamped and resized. Eventually Ill be adding the annealing process to the brass prep procedure on the caliber.