I purchased a PSA Gen 3 PA65 20" 6.5 Creedmoor (AR-10 platform) a few months ago and my initial focus was getting Optics mounted/zero'd, etc. I don't own a Chronograph but have been using a pretty accurate Ballistic Calculator and entering all parameters (including Environmentals) then doing rough velocity calculation based on groupings at 100 & 200 yards. What startled me was how much Velocity that I was losing as a result of the adjustable Gas Block being too open. It turns out, PSA ships this rifle with a Gas Block Factory Setting of 16-clicks open (5-clicks per rotation). Being a fairly new 6.5 Creedmoor shooter, it took me a while to realize the gun was severely over-gassed. Yesterday, I decided to follow YouTube video for adjusting Gas Block starting from fully-closed position. Before making Gas Block adjustments, my shells were expelling at 1 o'clock, recoil was obnoxious, and velocities were low. After making Gas Block adjustments, my shells are expelling at 4-4:30 o'clock, recoil has reduced quite a bit, and velocity has increased significantly. What I ended up with was a setting of 10-clicks open (from fully closed) to consistently expel my S&B 140 Gr FMJ at 4-4:30 o'clock. For margin, I opened Gas Block 1 additional click since I'm planning to shoot a variety of ammo from 130 Gr to 147 Gr (but most Match-Grade vs S&B). I'm now averaging somewhere around 2,580 fps out of the 20" barrel (was previously shooting 2,380 fps out of this barrel with Gas Block at 16-clicks open). Again, I don't have a Chronograph but believe I'm pretty close in my calculations. Has anyone else noticed a 200 fps increase in Velocity out of a 20" Barrel by simply adjusting the Gas Block? One final question, my shells expel about 15' out from the gun regardless of which direction, is this normal out of 6.5 Creedmoor?
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PSA Gen 3 PA65 20" 6.5 Creedmoor Gas Block & Velocity
- Thread starter macandrac
- Start date
IMHO, something else was causing your velocity changes. ( No offense )
Your gas port would have to be HUGE to lose 200FPS.
You are really going to need Chrono data, to assess velocities.
And as for the 15' ejection, is that with the Adj. GB adjusted at the more restricted point ?
A "standard" procedure for Adj. Gb's is a single mag fed round, fired, until you have reliable 100% consistent BCG lock back.
Then add one more click open.
Does your BCG have the "dual ejectors" ?
Your gas port would have to be HUGE to lose 200FPS.
You are really going to need Chrono data, to assess velocities.
And as for the 15' ejection, is that with the Adj. GB adjusted at the more restricted point ?
A "standard" procedure for Adj. Gb's is a single mag fed round, fired, until you have reliable 100% consistent BCG lock back.
Then add one more click open.
Does your BCG have the "dual ejectors" ?
No, I'm fairly confident the 200 fps gain in Velocity was due to adjusting the Gas Block - seems crazy but it's true. Yes, I followed the adjustment procedure to a tee (1 round loaded in Mag at a time) regarding adjustment and, yes, I added one additional click (as I mentioned in my original post) for margin. Yes, my BCG was designed with double ejectors. Finally, yes, the 15' is with Gas Block adjusted to 4-4:30 o'clock position (but that is on pavement, perhaps on gravel would be less).
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Not sure how many rounds you have through yours, but the Hornady American Gunner 140 BTHP chronograph 2473 through my 20" 6.5 PA10 during break in. Same lot of ammo measured 2648 last time out. My gun is now 2 years old and I have roughly 500-600 rounds through it.
Huh... I guess I don't know what to say.
And not questioning you guys results, just sure seems odd. And contrary to the norm.
I'm estimating that I have about 200-250 rounds through the gun so far - my Velocity was ~2,260 fps (4 weeks ago); ~2,380 fps (2 weeks ago), and ~2,580 fps (yesterday) so I think you are right that some of the increase in Velocity was attributable to barrel break-in but I do believe some was strictly the result of dialing back the gas. Thanks for providing me the data on your ammo and gun - that helps me out a lot. I've been shooting S&B 140 Gr FMJ for now (just because it is a quality round but on the cheaper side). I have purchased quite a bit of Hornady 143 Gr BTHP but haven't shot it yet.
If you don't have a chronograph then you have no idea what your velocity is . It's that simple . Looking at the velocity stated on the box is like letting your soon to be ex-wife write your divorce decree .
I'm not sure what you are talking about - I certainly never implied I was using the velocity off of a box. I think the issue here is that you are simply replying without reading what I've written. I'm going to make a wager with you - once my AR10 has settled down (based on velocities that I calculate based strictly off of ballistic calculator), I will then use a Chronograph and compare the Average Velocity to my computed Velocity based on Ballistic Calculator/Table. If the Velocity I compute is within +/- 5% of what the Chronograph Average Velocity is, you buy me 100 rounds of new 6.5 Creedmoor S&B 140 Gr FMJs. If I'm not within +/- 5%, I'll buy you 100 rounds of your favorite "Target" ammo (not Match grade stuff).
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Correct, but you can get darn close with POI at both 100 yards and 200 yards in same session - it's fairly simple to plug those POI's in and do reverse Velocity estimates. No, they aren't exact but I experienced substantial shifts.
Calculating the velocity using POI difference between 100 and 200 yards is absurd. No one would need to buy a crono then.
Think about it, you claim that you closed the gas block valve (reducing the pressure bleed off from the barrel) and the velocity
decreased then you opened the gas block valve (increasing the pressure bleed off from the barrel) and your velocity increased?
I thought he said the opposite of that, which in theory would be correct, but not 200fps, without a chrono, based on close range POI variation correct.
The way it is written he claims he started with a closed gas block.
"I decided to follow YouTube video for adjusting Gas Block starting from fully-closed position. Before making Gas Block adjustments, my shells were expelling at 1 o'clock, recoil was obnoxious, and velocities were low."
I understand this to mean he started to open up the gas block.
"After making Gas Block adjustments, my shells are expelling at 4-4:30 o'clock, recoil has reduced quite a bit, and velocity has increased significantly."
So I dont know.
Well now I'm just confused. Regardless, the gas block adjustment method is the least silly thing going on in here.
