375 H&H project barrel chop w/ velocity data

[samson7x]

I just wanted to post this mini project for folks who are interested in chopping their barrels and what that might mean for velocity loss. There seems to be much discussion regarding this as well as suppressor use so I took chrono results pre and post chop with several different factory loads for real world data. Keep in mind, this is in my rifle so your results may vary to some degree.

Rifle: New production Winchester M70 in 375 H&H
Chrono used: Garmin Xero @ 540ft elevation
Original barrel length: 25”
Barrel length after gunsmithing: 20”
Gunsmith used: Long Rifles Inc in SD
Modifications: Threaded 5/8-24 with flare for adequate shoulder, front sight relocated
Suppressor: Thunderbeast Magnus S-RR with custom flat front cap which is interchangeable with the RR brake
I installed timney trigger set to 2lbs
Optic used for accuracy data: Leupold mk5 3-18
Optic will be swapped with a Trijicon accupoint 1-8 for field work.

As compared to my mountain rifle Seekins havak element with 21” barrel and ultra 5 suppressor:

Weight as pictured:

Custom shoulder flare for suppressor use:

How much total length did I add with suppressor?

Custom end cap:

 

[samson7x]

Saved for velocity data

 

[Knoxp9090]

Super excited to see the results.

I'm thinking of doing this with my Montana 1999 - .375

 

[samson7x]

Saved for velocity data

I guess I exceeded the time limit to edit…


Velocity data:

Federal 300gr swift A frame
25” - 2509
20” - 2418
Delta of 91 or 18.2 per inch
Avg group size: 0.85”

Barnes 300gr TSX
25” - 2542
20” - 2447
Delta of 94 or 18.8 per inch
Avg group size: 0.86”

Hornady 300 DGX
25” - 2616
20” - 2476
Delta of 140 or 28 per inch
Avg group size: 2.05”

I was only able to acquire these loads after the chop but thought it worthwhile to add here:

Federal 300gr trophy bonded bear claw
20” - 2467
Avg group size: 1.41”

Pendleton 300gr Swift A frame
20” - 2607
Avg group size: 1.2”
*only 3 groups calculated in accuracy avg


So key take aways for me were that velocity is not as affected as most folks believe. Hornady DGX had the greatest velocity loss and worst accuracy for me. Pendleton’s load was as fast or faster at 20” than the others at 25”. I only had 3 groups recorded for Pendletons average. I still want to test this a bit more and try their Barnes load. I may start dabbling in handloads to see what I can get.

 

[JeeperCreeper]

Amazing, thank you!

 

[RedTag]

I guess I exceeded the time limit to edit…


Velocity data:

Federal 300gr swift A frame
25” - 2509
20” - 2418
Delta of 91 or 18.2 per inch
Avg group size: 0.85”

Barnes 300gr TSX
25” - 2542
20” - 2447
Delta of 94 or 18.8 per inch
Avg group size: 0.86”

Hornady 300 DGX
25” - 2616
20” - 2476
Delta of 140 or 28 per inch
Avg group size: 2.05”

I was only able to acquire these loads after the chop but thought it worthwhile to add here:

Federal 300gr trophy bonded bear claw
20” - 2467
Avg group size: 1.41”

Pendleton 300gr Swift A frame
20” - 2607
Avg group size: 1.2”
*only 3 groups calculated in accuracy avg


So key take aways for me were that velocity is not as affected as most folks believe. Hornady DGX had the greatest velocity loss and worst accuracy for me. Pendleton’s load was as fast or faster at 20” than the others at 25”. I only had 3 groups recorded for Pendletons average. I still want to test this a bit more and try their Barnes load. I may start dabbling in handloads to see what I can get.

Excellent work. Thanks for sharing. I don’t have any interest in suppressors personally but this kind of information is really valuable. And it goes to show we can’t ever know for certain how an individual rifle and/or load is going to perform until we actually put it to the test. I really enjoy chronograph testing.

 

[kdenn]

Thanks for sharing this information. I’m contemplating doing the same.

 

[spike.t]

So the after were with the suppressor in place?....if so any idea what the difference is without using it..or won't it make any difference?

 

[samson7x]

So the after were with the suppressor in place?....if so any idea what the difference is without using it..or won't it make any difference?

Yes, after threading I only shot it with suppressor and RR brake attached. From what I’ve read, it should have minimal impact on velocity with these relatively slower rounds and particularly with the endcap brake bleeding gas as it exits. However, that would be interesting data to add at a later date.

 

[Odinsraven]

Doctari said 2400 was perfect for the 375 - he loaded to that - He is sometimes around here, Doctari505 if my memory serves me correctly !

I guess I exceeded the time limit to edit…


Velocity data:

Federal 300gr swift A frame
25” - 2509
20” - 2418
Delta of 91 or 18.2 per inch
Avg group size: 0.85”

Barnes 300gr TSX
25” - 2542
20” - 2447
Delta of 94 or 18.8 per inch
Avg group size: 0.86”

Hornady 300 DGX
25” - 2616
20” - 2476
Delta of 140 or 28 per inch
Avg group size: 2.05”

I was only able to acquire these loads after the chop but thought it worthwhile to add here:

Federal 300gr trophy bonded bear claw
20” - 2467
Avg group size: 1.41”

Pendleton 300gr Swift A frame
20” - 2607
Avg group size: 1.2”
*only 3 groups calculated in accuracy avg


So key take aways for me were that velocity is not as affected as most folks believe. Hornady DGX had the greatest velocity loss and worst accuracy for me. Pendleton’s load was as fast or faster at 20” than the others at 25”. I only had 3 groups recorded for Pendletons average. I still want to test this a bit more and try their Barnes load. I may start dabbling in handloads to see what I can get.

5

 

[Andrew62]

I guess I exceeded the time limit to edit…


Velocity data:

Federal 300gr swift A frame
25” - 2509
20” - 2418
Delta of 91 or 18.2 per inch
Avg group size: 0.85”

Barnes 300gr TSX
25” - 2542
20” - 2447
Delta of 94 or 18.8 per inch
Avg group size: 0.86”

Hornady 300 DGX
25” - 2616
20” - 2476
Delta of 140 or 28 per inch
Avg group size: 2.05”

I was only able to acquire these loads after the chop but thought it worthwhile to add here:

Federal 300gr trophy bonded bear claw
20” - 2467
Avg group size: 1.41”

Pendleton 300gr Swift A frame
20” - 2607
Avg group size: 1.2”
*only 3 groups calculated in accuracy avg


So key take aways for me were that velocity is not as affected as most folks believe. Hornady DGX had the greatest velocity loss and worst accuracy for me. Pendleton’s load was as fast or faster at 20” than the others at 25”. I only had 3 groups recorded for Pendletons average. I still want to test this a bit more and try their Barnes load. I may start dabbling in handloads to see what I can get.

This is some very valuable information, thank you for taking the time to do this test then letting the rest of us know! I have had the barrels of both my .375H&H and 416 Rigby cut down to 20". I much prefer the shorter barrel.

 

[BANDF]

Thanks for taking the time to do this!

You've confirmed what is widely known within the internal ballistics field. Larger bore diameters have significantly less velocity loss for a given length reduction, given their considerable bore volume for combustion/burning of the powder... the inverse is true for the smaller bore diameters - you're simply reducing a greater proportion of bore volume relative to length to aid in powder burn.

 

[spike.t]

Yes, after threading I only shot it with suppressor and RR brake attached. From what I’ve read, it should have minimal impact on velocity with these relatively slower rounds and particularly with the endcap brake bleeding gas as it exits. However, that would be interesting data to add at a later date.

Yup be interested to see what if any difference...please do when /if you can....my 500 jeffery has 20 inch barrel....not apples to apples as liked to be used on here but be interesting to see...