New to ARs here. Acquired a Seekins SP10 in 6.5 CM. If the Hornady 140 ELDM box states 2710 fps in a 24” barrel, I assume that’s a bolt action. In a gas gun, what would that velocity be? I’m shooting a 22” barrel and reading I might expect a 40-50 fps drop due to 2” shorter barrel. I don’t have a chronograph but shoot 100-200 yd groups and infer initial velocity from that drop. I realize a 100-300 yd drop would yield a more accurate inference but don’t have easy access to 300 yds. So I’m wondering how fast these 140 ELDMs are leaving my barrel? So is it expected to lose velocity for 2 different reasons: gas vs bolt and shorter barrel? If anyone has chronographed their 6.5 CM Seekins SP10 without suppressor shooting 140 ELDMs, I would be very much interested in their results. Thank you.
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Bolt gun velocities vs gas gun velocities?
- Thread starter rmiked
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I have a 6.5 CM bolt gun and a AR 10 both have 24" barrels.
24" barrels... auto vs bolt depends on the powder and bullet combinations... but one load was 14 fps difference and the other 20 fps difference with the higher velocities going to the bolt gun of the same barrel length.
So it ain't much.
Two bolt guns with barrels of the same length could have that much difference.
These were handloads with 150 gr SMK bullets, with 2 different powders RL 26 and Superformance...and that was the result.
Probably expect something like 15 to 40 fps difference from the majority of ammo, between the two action types, in favor of the bolt action.
24" barrels... auto vs bolt depends on the powder and bullet combinations... but one load was 14 fps difference and the other 20 fps difference with the higher velocities going to the bolt gun of the same barrel length.
So it ain't much.
Two bolt guns with barrels of the same length could have that much difference.
These were handloads with 150 gr SMK bullets, with 2 different powders RL 26 and Superformance...and that was the result.
Probably expect something like 15 to 40 fps difference from the majority of ammo, between the two action types, in favor of the bolt action.
Man you could lose or gain velocity between two near identical 22" barrels regardless of the action type. While barrel length and action type play a part in it some barrels also speed up after a couple hundreds, plateau for a bit, and then lose velocity as the throat wears out. On top of that you're contending with lot to lot variations in the factory ammunition itself which is another factor, there's no way to definitively say "your velocity will be this...".
Inside of 300 yards though the velocity of a 6.5CM doesn't matter much, I'd say even out to 500 yards you can be pretty far off and still get a hit on a 10"-12" plate with ease. At 2,700 fps your 300 yard dope is about 1.1 mils / 3.75 MOA and at 2,600 fps you're looking at 1.2 mils / 4.0 MOA. At 500 yards a 140 at 2,600 fps needs 3.0 mils / 10.5 MOA and at 2,700 fps it's 2.7 mils / 9.5 MOA, that equates to a 5" difference in trajectory. (Edited for correction because I couldn't do the maths)
Best advice I feel I can give is keep a data book, log your data, and go from there. Check out Gravity Ballistics here on the Hide.
Inside of 300 yards though the velocity of a 6.5CM doesn't matter much, I'd say even out to 500 yards you can be pretty far off and still get a hit on a 10"-12" plate with ease. At 2,700 fps your 300 yard dope is about 1.1 mils / 3.75 MOA and at 2,600 fps you're looking at 1.2 mils / 4.0 MOA. At 500 yards a 140 at 2,600 fps needs 3.0 mils / 10.5 MOA and at 2,700 fps it's 2.7 mils / 9.5 MOA, that equates to a 5" difference in trajectory. (Edited for correction because I couldn't do the maths)
Best advice I feel I can give is keep a data book, log your data, and go from there. Check out Gravity Ballistics here on the Hide.
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Nice, I use those plus my Kestrel and Strelok Pro, I still like to keep a data book and Gravity Ballistics is nice to have in the toolbox too.
A book? You mean write shit down??? You must be one of them ol’ timers…
Beg or borrow a chronograph to get real actual numbers. Going by the number on the box or the website is meaningless and guessing at the difference due to barrel length is too. Someone you know has to have a chrono....real numbers get you real data, guessing gets you ?
Frank
Frank
I like to keep it old school, I've just started using this electronic mail thing and heard that everyone is starting to use these metric scopes now....so I'll need to look into that too. Crazy times man.
Don't let em make a communist out of you with them newfangled mm scopes. Make MOA Great Again
I have a SP-10 6.5C and get 2752 from my 22" barrel in South Florida. It is a hand loaded 140 ELD-M, but I built the load to match Factory velocity out of my MPA rifle so I could use either in matches. Should be close to what you will get. Close to sea level and usually 70 degrees.
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It would be my guess you would drop 50 fps going from Bolt to gas and dropping 2 inches. But that its purely a guess. My 24' Bergara Bolt guns gets 2700-2725 fps 140 ELD's ( right on with posted data) in my bolt gun. Typically a little drop with my 20 inch MWS. I just got my Garmin so my testing is starting to be extensive. Our handholds do better, last time we tested 143's out of the gasser we 2725. Shorter barrel and gasser but thats handholds. You might have a tight bore and fast gun, you never know.
But without testing your barrels and guns, you could gain velocity?? Lotta help but that is what you get with those inputs, guesses. Go get a Garmin if possible and life will be better.
PB
But without testing your barrels and guns, you could gain velocity?? Lotta help but that is what you get with those inputs, guesses. Go get a Garmin if possible and life will be better.
PB
So in general, a suppressor increases back-pressure and slows down a bullet? I have read a suppressor results in needing less gas to operate the BCG so adjusting the bas block more closed is necessary. I was unaware it might slow down the bullet? Based on your numbers you are getting excellent velocities with a suppressor.
Who uses bolt guns? They’re relics from the 1800’s. Maybe the Amish?
Suppressed may increase velocity a very minimal amount. I haven't tested myself but heard 1-10fps increase from some people.
I tested two guns today with and without a suppressor. One an LMT 10.5 and the other a Bergara 6.5CM. Both increased velocity 10/11 fps with the can on. Or decreased velocity with can off. I think this is the general consensus but every barrel and suppressor can be different.
I also tested some gas guns and I dont think being a gas gun loses velocity as much usually the barrel length is the cause of lower velocities. I shot my MWS with factory Norma 175's and the box said 2593 FPS (which is usually tested with 24 inch bolt gun barrel) and my gun did 2531 fps. 61 FPS slower and 4 inches shorter, I would have guessed more loss. You never know until you know.
Again, good luck with your blaster.
PB
I also tested some gas guns and I dont think being a gas gun loses velocity as much usually the barrel length is the cause of lower velocities. I shot my MWS with factory Norma 175's and the box said 2593 FPS (which is usually tested with 24 inch bolt gun barrel) and my gun did 2531 fps. 61 FPS slower and 4 inches shorter, I would have guessed more loss. You never know until you know.
Again, good luck with your blaster.
PB
