Short Barrel Rifle Question?

CaptnC

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Just built a 10.5" 6.5 Grendel pistol, that should next month become a suppressed SBR.

But for now it's got my suppressor from another AR and is in a pistol configuration.

I actually have a few questions;

Will swapping suppressor's change the load I have for it? Both suppressors are made by the same company and same model.

I know the reduced barrel length, reduces velocity but I have made some odd observations. Looks like 2200fps is all I will get out of my barrel. Regardless of bullet and powder combinations.

90gr TNT, 100gr NBT and 107gr TMK all came in 2100fps to 2200fps...the SD and ES were so close, just looking at the numbers on my Magnetospeed you would think it's a tuned load.

Is load development senseless on a short barrel?

Finally, I attached my Magnetospeed to the suppressor.

20200628_152011.jpg

Of course I had to change the settings to get it to sense the bullet fight.

How reliable will the readings be using the Magnetospeed in this fashion?
 

J E Custom

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Different suppressors can effect the gas guns (Like the AR's) Because the port pressure will/can change. I would also move the Magneto speed farther out where the muzzle is near the back half of the curved part of the bayonet. (It allows for a better separation of gas and bullet for more accurate readings).

It is also not unusual for short barrels not to respond to velocity changes when using rifle powders.

J E CUSTOM
 

CaptnC

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Thanks J E for the tips. I never thought about trying a pistol powder in a barrel this short.

The best place I guess to ask about a pistol powder is over at 6.5grendel.com but dang I hate to let some of those guys know I own a Grendel with this short of a barrel. I've beat the short barrel horse to death over there! LOL

At this time there is not much powder available so I doubt if I could find any pistol powder right now....so I guess I will roll with a rifle powder for now.
 

J E Custom

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Thanks J E for the tips. I never thought about trying a pistol powder in a barrel this short.

The best place I guess to ask about a pistol powder is over at 6.5grendel.com but dang I hate to let some of those guys know I own a Grendel with this short of a barrel. I've beat the short barrel horse to death over there! LOL

At this time there is not much powder available so I doubt if I could find any pistol powder right now....so I guess I will roll with a rifle powder for now.

There are faster burning rifle powders for heavy bullets that will work, (like H335) If you find the right one. I would also recommend an adjustable gas block to regulate/tune the port pressure if used in an AR.


J E CUSTOM
 

CaptnC

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It has an adjustable gas block already. I have plenty of H335...I've had good results with it in my other Grendel AR's.

Thanks J E
 

Gord0

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I'm not a short barrel fast powder guy. You'll get the best velocity from the best powder for that bullet weight regardless of barrel length. That being said, with a suppressor, the faster powders will have less of a difference in port pressure with it attached vs unattached. This being due to less gas pressure in the suppressor. H335 may be your huckleberry.
 

WGTX

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I don't have a Grendel but I do have 3 6.8 SBRs & 2 30 cal Saker cans. I've never seen a noticeable poi shift swapping the 2 cans on the SBRs or bolt guns for that matter.
 

CaptnC

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To be honest I have never shot this SBR without the suppressor. So I have no clue if it had a POI shift.

I don't have my notes in front of me this minute, but I had several different bullet/powder combos with me and shot them all. But I recall many that did hit 2200fps.

The main reason I have gone suppressed is so the wife and I can hunt together without ear protection. I know you should always wear ear protection, but it's normally only single shot. She is fairly new and I normally talk to her leading up to the actual break of the trigger. This past weekend we were hunting hogs, I took a shot at a raccoon and the little beast rang our ears.

So the SOS Hunter I have now doesn't adequately suppress a 10.5" barrel 6.5 Grendel.

Hence my other thread about a Form 1 suppressor. I believe a combination between reworking my load and a high baffle count suppressor will yield the results I want. If that suppressor doesn't work I will move it to another rifle and do another form 1.

When I say "reworking" I'm going to reduce one of the 2200fps loads until it drops under 2200fps. I believe 2200fps is all you can get out of that much barrel regardless how much powder you stuff in the case. So I basing my thoughts on the idea that there an excess of powder in those cases. So I feel I can lessen muzzle blast to help the suppressor do it's job.

This is all based off my little brain working and not research based...so if I'm way off base, feel free to clue me in!
 

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