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Posted: 10/5/2014 6:05:24 PM EST
[Last Edit: 10/5/2014 6:10:44 PM EST by delirious1]
An observation this weekend. I tested 5 rounds of various ammo suppressed and unsuppressed with chronograph. I noticed that all rounds tested increased in varying degrees suppressed vs unsuppressed. 10.3, 10.5, and 16 inch barrels were tested and it was noted that the degree if speed increased with barrel length. I would expect that. Speed increases were small. I averaged the 5 loads suppressed and unsupressed and subtracted the results. I got 170 FPS difference through my 16 inch barrel. Something to consider. Using a 70 grain Barnes TSX, my loads were two inches low suppressed at 50 yards. Suppressor was SDN6 and host was a 16 inch DD 1:7. 10.3 was DD 1:8. And 10.5 was a Noveske 10.5 switchblock CBQ

Handloads tested:
Barnes 110 gr tac tx supersonic
SMK 220 grain subsonic
Barnes 70 grain TSX supersonic
Gemtech 187 gr subsonic
125 grain SMK supersonic

Anyone else want to share their findings?

I think this is important for not only shift but for working up subsonic loads. Speeds will increase if you are on the edge of subsonic and you go suppressed.
Link Posted: 10/5/2014 8:16:26 PM EST
[Last Edit: 10/5/2014 8:20:56 PM EST by goloud]
Interesting. That's a big difference in velocity. I'm assuming 300blk?

A five round sample size probably isn't enough to make a determination solely on the silencer affecting velocity. For instance:

* Was the bbl warm for one string and cold for another?

* Indoors or outdoors? Environmental changes?

* Did you clean your bbl between strings?

* Confidence in the repeatability of your reloads? Randomly mixed batches, etc?

170fps spread is a lot. Almost like adding/subtracting 2-3in of bbl length.

I don't have enough experience testing velocities suppressed vs unsurpressed, so I'm not disagreeing with you. I just think other variables might need to be looked at before making a decision.

ETA: I'm also not sure where that extra velocity would be coming from. Once the tail of that bullet crosses the crown, suppressor on or not, aren't we done pushing that bullet out?
Link Posted: 10/5/2014 9:13:33 PM EST
Link Posted: 10/5/2014 9:33:04 PM EST
Its called "suppressor push" if memory serves me correctly. The suppressor tube acts to marginally increase velocity.
Link Posted: 10/5/2014 10:42:26 PM EST
[Last Edit: 10/5/2014 10:44:26 PM EST by AK_Mike]
It's called Free Bore Boost.

You are still generating gas pressure from propellents behind the bullet while there is no friction on the bullet, thus increasing your velocity.
Link Posted: 10/5/2014 10:57:55 PM EST
Thanks guys. Most all my tests were same temperature. Load 5. Shoot 5 with a few seconds apart. Next 5 within 1-2 minutes just to label the series on the iPhone. I'm using the Caldwell chrono. I'd then change uppers and repeat. Not scientific. It was more an observation while testing my hand loads.
Link Posted: 10/6/2014 5:57:02 AM EST
Awesome. I learned something and I guess I shouldn't have been so skeptical.

Good stuff. Drive on.
Link Posted: 10/6/2014 6:59:22 AM EST
Yes it's real, It varies based on barrel and ammo type but was always told around 100 fps velocity increase
Link Posted: 10/6/2014 10:35:45 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Spartikis:
Yes it's real, It varies based on barrel and ammo type but was always told around 100 fps velocity increase
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I think that figure may be way off. In general, with barrel length you get 10 fps per inch per 1,000 fps initial velocity. Therefore, a subsonic round will gain 100 FPS with a 10" change in barrel length. A 5.56 should gain 100fps with about 4" of barrel length change. I may be wrong, but I don't think 100 FPS sounds right for a velocity increase. Haven't tested it myself... but I will... and post a video!
Link Posted: 10/6/2014 10:55:39 AM EST
[Last Edit: 10/6/2014 11:03:12 AM EST by delirious1]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BadgerArms:

I think that figure may be way off. In general, with barrel length you get 10 fps per inch per 1,000 fps initial velocity. Therefore, a subsonic round will gain 100 FPS with a 10" change in barrel length. A 5.56 should gain 100fps with about 4" of barrel length change. I may be wrong, but I don't think 100 FPS sounds right for a velocity increase. Haven't tested it myself... but I will... and post a video!
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View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BadgerArms:
Originally Posted By Spartikis:
Yes it's real, It varies based on barrel and ammo type but was always told around 100 fps velocity increase

I think that figure may be way off. In general, with barrel length you get 10 fps per inch per 1,000 fps initial velocity. Therefore, a subsonic round will gain 100 FPS with a 10" change in barrel length. A 5.56 should gain 100fps with about 4" of barrel length change. I may be wrong, but I don't think 100 FPS sounds right for a velocity increase. Haven't tested it myself... but I will... and post a video!


my biggest leap was 170 fps with a 16 inch 556 daniel defense barrel 1:7 with a Barnes 70 grain TSX. I didn't see such big leap with subsonics out of the 300 blackout. That was anywhere from 8 FPS to 50 FPS, but no more. That was with suppression vs nonsuppression, same barrel. Yes, I would assume if I tried the subsonics on a 16 inch barrel, it would increase. But I don't have a 300 blackout with a long barrel to test.

I made mention to all of this because I've read other posts saying suppressed increased speed, but didn't say by how much. I can just confirm for just the knowledge that it does. ....and application is where you are on the fence of reloading between super sonic and sub sonic speeds. A suppressor may send you over. I don't think speed has to do with suppressor POI shift as much as barrel harmonics.


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