Home Forums Hunting & Shooting Hunting Rifles Shortened barrel = increased velocity

I recently had a 243 Rem 700 ADL barrel chopped from 24 to 21.5 inches. I was expecting to lose about 75-100 fps but surprisingly gained a little velocity with the same loads! Handling of the rifle was more important to me than a little velocity lose, I’ve shortened other barrels before but never did a pre and post ‘surgery’ comparison.

I’ve had the rifle for a ~ 1.5 years and had established loads with H4350 and two bullets; 87 vmax & 95 ballistic tip. The same can of H4350 was used for all the velocity reading pre and post barrel shortening so it is not a powder lot difference. New velocities were taken on two separate range trips and temps were also very similar according to my notes - same ProChrono too. After cutting to barrel the 87 vmax gained ~50 fps (43 g H4350, Hornady case, CCI 200), the 95 BT gained about 60 fps (41g H4350, Hornady case, CCI 200).

I assume the barrel may have had an oversized portion near the muzzle or decreased friction accounts for the increase. Whatever it is, the increase is there. Just shows that sometimes ‘established’ rules don’t hold true in the real world.

Try a slower powder and you may find what you were looking for.

Did you even read his post

Yes, Kaleb. As a matter of fact I did.

It's illogical.

The reason lies elsewhere.

So....your logical explanation?

How many shots were sampled during each range session?

A dozen with the Ballistic tips. More with the 87 Vmax but I am not exactly sure the exact total.

After the first session I was seriously doubting the readings so put I in a new battery in the chrony, loaded up some more rounds, and checked again the following week. Temps were in the 70's both days and the chrony was in the shade.

I'm just reporting what I observed in this rifle as it was unexpected.

Once the powder is fully burned, any remaining barrel length is just friction slowing down the bullet.

Every barrel/bullet/powder/cartridge combination has an optimum length.


So, this makes perfect sense.

djb,

A slight velocity increase when shortening barrels has been recorded many times before. Phil Sharpe saw it in his experiments decades ago, when he shortened barrels an inch at a time and shot at least 10 rounds (as I recall) at each length. He attributed it, as you guessed, to slightly tighter and looser sections in the bore, something that's not uncommon in barrels.

In principle, I agree, but your first statement isn't quite right. After the powder is fully consumed the hot gases continue to expand and accelerate the bullet until pressure drops below the threshold required to accelerate the bullet, which I believe is below 2,000 psi in most cases (I believe MD has mentioned that it takes about 2,000 psi to engrave a bullet, which is more than the pressure necessary to accelerate the bullet once it's beyond the throat).

I don't feel compelled to speculate on some half assed backyard test based on a sample of "one",conducted outside a ballistics lab, so I will leave it to you to figure out.Like most such "tests" we read about here and taken as gospel based on sketchy evidence and samples of one, mostly it's BS.

I don't believe in ballistic anomalies.

But here's a few hints: different day, different lighting conditions, different humidity,different primer,and inaccurate unit(Pro Crony? Gimme a break). I've used enough of them in my day long with Oehler. They tell me "rough numbers" but I never assume they are gospel.They will vary day to day.

In order for the these results to be correct the bullet would have to have achieved max velocity at 21.5" before the barrel was cut....right? And then slowed down.....right? That make sense?

I doubt it. Illogical.

I still don't buy it.

It should make sense for a guy born in the blackpowder era.

I'm more progressive than that....you ain't far behind me.

I'm way ahead of you.

I am pretty sure that's not correct since the gas from the burning powder continues to exert force on the base of the bullet until it exits. Your entire barrel is the combustion chamber. How much varies with the type of powder.

That's how we get muzzle pressure, right?



I guess the new formula for higher velocity in your 300 Weatherby Mag is.....if you have a 26" barrel, cut it to 22".....makes sense to me.

Where's the hacksaw?

Yep

I cut my 7x57 from 24 inch's to 21 inches and lost only 9 fps with the same load of H4831 and the Hornady 162 gr A-Max

I wouldn't be at all surprised if the velocity loss were very small.

I wouldn't be at all surprised to see an individual 21.5" barrel shoot faster than a different 24" barrel. In fact I've seen it happen.

I wouldn't be at all surprised to see over 100 fps difference between 2 different barrels of the same length. I've seen that happen too.

I would be very surprised to see a barrel gain velocity after it were cut. I suppose it could happen, but my guess is that the speeds measured either at 24" or 21.5" were off very slightly. In reality you probably lost very, very little speed. I think it was small enough that your testing tools or methods weren't accurate enough to catch the difference and it appears you gained speed.

I don't care what you buy Bob. These boards are for sharing info. I wasn't setting out to test any theory, I just wanted to see what velocity the shortened barrel cost me. As I said... "I'm just reporting what I observed in this rifle as it was unexpected."