9mm Accuracy & Velocity

Everything that I've read on this forum indicates that 9mm has to be pushed fast to be accurate.  Why is this when .45 ACP and .38 Special seem to perform fine at much lower velocities?    This doesn't make sense to me.

Velocity increase equals higher rpm which plays a major role in stability.The 1x32 twist 9mm is a good example. A 10/12 twist 38 SPL will shoot quite well at 700 fps. because the rpms are higher from the faster twist even at low velocity.

Following up on what Jerry said. A bullet fired out of a 9mm with a 1x32 twist will revolve about 168 times in 50 yds. The 38 ( with a 1x12) would revolve about 450 times. If you fire the 9 with a MV of 700 fps it will revolve about 168 times. If you fire it at 1400 fps it will revolve about 168 times. Sounds the same. But, it does it in half of the time. In effect doubling its rpms which is a measurement of time not distance. That still only brings it up to only a little over 2/3 of the revolutions of the 38. I think that is one of the reasons a lot of people don't like 9's. I rounded numbers and didn't allow for drag, bc, gravity etc but those numbers are close enough for government work.

Len

A 115 gr JHP at 1100 fps is very stable and accurate in most 9mm.  This is a minor power factor load, so shoots soft enough for IDPA game gun type matches.  I used a 9mm in bullseye all of 2014 with good results, with this relatively soft load for a 9.  I can certainly see where going to an even lighter load, say at 900 fps, might start getting too slow and creating problems.  I've shot my 9mm gun from a rest at 100 and 200 yards several times with excellent results using this cartridge.  I have not tried the 147 gr bullet at the same distances.  The twist rate plus the rotating moment of inertia of the hollow point plus velocity all come in to play here, I think.
Joe

There is another opinion ttht it is an issue with muzzle and target velocity. Unfortunately most 9 loads start out supersonic at muzzle and are dropping in subsonic between 25 and 50. That transition can create accuracy issues. Thats why you might get good groups with factory at 25 but not at 50. So the accuracy loads are hotter for the 9 if you are looking for good 50 yd groups. Or you can go with heavier bullets and sub velocities, to keep the recoil impulse the same for pistol functioning. Or go to lighter springs. Just stay away from loads that transition to sub sonic before getting to the target.

if a 1in12 twist barrel means the bullet revolves one time in 12 inches (1 foot) and the 50yd target is 150 feet away the 38 revolves 150 times on its way to the target.  A 1in32 twist barrel would revolve 56.25times (distances in inches divided by the twist rate in inches).  Where do the extra revolutions come from?  450 for the 38 and 168 for the 9mm

Scott

Gentlemen, just my 2 cents worth. I don't think that's how it works.
It's not just the twist rate that determines the rpm. You have to factor in the bullet velocity, barrel length...  Google bullet rpm calculator.

                                             Walt

I didn't say RPM.  I posted revolutions to 50 yds which is what Oldmaster posted.  My quick rpm calculations were like 42,000 for the 38 and 24,000 for the 9mm.

Scott

SMBeyer wrote:if a 1in12 twist barrel means the bullet revolves one time in 12 inches (1 foot) and the 50yd target is 150 feet away the 38 revolves 150 times on its way to the target.  A 1in32 twist barrel would revolve 56.25times (distances in inches divided by the twist rate in inches).  Where do the extra revolutions come from?  450 for the 38 and 168 for the 9mm

Scott

The extra rpms come in because I was doing it way to late at night. I think I took 50 x 3 x 36 instead of 50 x 3 x 12. My bad. Same ratio. Bad math. Sorry.

Len

What the difference between revolutions and rpm's to the target?

In a post several months ago I asked some of these same questions.  It boiled down to this: If the 38 Special using a 148 wadcutter at 700 fps out of a 10-12 twist barrel is extremely accurate as shown by the PPC builders, why wouldn't the 9mm using a 147 grain bullet at 700 fps also show good accuracy out of a 10-12 twist barrel?  The primary issue in trying to answer this experimentally is the lack of 9mm 1911 barrels in 10 or 12 twist.  Jerry Keefer provided me with a section of Douglas 9mm 12 twist barrel blank which I have used to sleeve an existing 9mm barrel.  I have completed the build and am now in the testing stages.  It is too early yet, but I plan to report on my results with this project after more thorough testing.  It looks promising so far.

According to Springfield's 2014 catalog the twist rate for both the .45 ACP and 9mm barrels is 1:16.  So borrowing from Dr.Don's post can I expect the same accuracy out of the 9mm as with the .45 using loads delivering the same velocity?  If not, what other factors come into play?

beeser wrote:According to Springfield's 2014 catalog the twist rate for both the .45 ACP and 9mm barrels is 1:16.  So borrowing from Dr.Don's post can I expect the same accuracy out of the 9mm as with the .45 using loads delivering the same velocity?  If not, what other factors come into play?

You missed the part about bullet weight, and the 2 bullets (.38 and 9MM) are nearly the same diameter.

- Dave

Beeser if you want a accurate 9mm, get tony kidd or david sams to build you one, nothing off the shelf that Springfield or others sells will do what you want. I shot and scored next to James Henderson, he shot a 886 cf with his 1911 9mm using Atlanta arms 115 xtp -hp rounds, it was very accurate but that's also out of the hand of a national champion.

This is an interesting topic for a variety of reasons.  After thumbing through The Pistol Shooter's Treasury by Gil Hebard, it's obvious that the 9mm didn't have a significant impact on Bullseye, at least early on.  Since tradition seems to play a major role in what happens in this sport it's no surprise that 9mm is relatively slow in catching on despite its major use elsewhere.  I suspect this may be changing.

DavidR wrote:Beeser if you want a accurate 9mm, get tony kidd or david sams to build you one, nothing off the shelf that Springfield or others sells will do what you want. I shot and scored next to James Henderson, he shot a 886 cf with his 1911 9mm using Atlanta arms 115 xtp -hp rounds, it was very accurate but that's also out of the hand of a national champion.

No doubt but it seems to me that I should at least get the same accuracy out of the 9mm as the .45 ACP RO, especially since they are essentially the same pistol with the same barrel twist rate.  The bullets used also have the same physical characteristics.  Do we have an issue here with giants and Lilliputs scaling?

Even with equal accuracy, the .45 holes are bigger and nicer and score higher than 9mm!!

Here is a recent 100 yard video from a CZ P-09 using Atlanta Arms 115 JHP that will illustrate what is possible.  I didn't place the first shot well in the sight, but the next 4 are pretty tight.  This is with my plastic P-09 bullseye gun. 

ok, let me ask a  question, IF you could get the same  accuracy out of your 9mm ro as a 45 ro, the velocity of the 9mm has to be much greater which makes for in some cases more recoil then where exactly is there any benefit to using one for bullseye? Not even factoring in the bullet size and scoring of the shot, a 9mm (.355 dia) that impacts the target in the same spot a 45 (.452) does if within .097 of a scoring ring will score 1 point less.

Joe L wrote:Even with equal accuracy, the .45 holes are bigger and nicer and score higher than 9mm!!

Here is a recent 100 yard video from a CZ P-09 using Atlanta Arms 115 JHP that will illustrate what is possible.  I didn't place the first shot well in the sight, but the next 4 are pretty tight.  This is with my plastic P-09 bullseye gun. 

very impressive! The accuracy of that ammo is outstanding, its the ammo of choice for anyone shooting a 9mm in bullseye.

DavidR wrote:ok, let me ask a  question, IF you could get the same  accuracy out of your 9mm ro as a 45 ro, the velocity of the 9mm has to be much greater which makes for in some cases more recoil then where exactly is there any benefit to using one for bullseye? Not even factoring in the bullet size and scoring of the shot, a 9mm that impacts the target in the same spot a 45 does if within .094 of a scoring ring will score 1 point less.

That's the crux of the problem or question.  It was mentioned earlier that 9mm has to be pushed faster than .45 ACP to compensate for the differences in twist rate.  But in the case of the RO the twist rate for both 9mm and .45 ACP are the same.  So, in order to achieve the same accuracy, why does the 9mm have to be pushed faster?  I realize there's a practical consideration in using .45 over 9mm for scoring but it has nothing to do with the original question.  I'm obviously still learning and this is just another question that popped into my head.

Hi Beeser

Some educated guesses on my part.

Bullet Circumference and bullet weight are likely the factors for the difference in accuracy between the .45 and 9mm out of the range officer.

 
Also, 9mm is also a higher pressure round and smaller case which tolerates less variation than the large .45 or longer .38 special when reloading.

This is all fine and good but what about the 1:10 twist of the 9mm SIG pistols?

Trans-sonic velocities are more relevant for wind drift than total accuracy with these shorter, low-BC bullets. They just aren't like the 150-gr M2 Ball bullet, which I have seen go sideways at 600 yards.

It also seems, to me at least, that match-tuning a Beretta is a lot more trouble than tuning up a 1911. That probably has nothing to do with the ammo, though.

I think something else is up, other than twist rate and RPM values.

DavidR wrote:Beeser if you want a accurate 9mm, get tony kidd or david sams to build you one, nothing off the shelf that Springfield or others sells will do what you want. I shot and scored next to James Henderson, he shot a 886 cf with his 1911 9mm using Atlanta arms 115 xtp -hp rounds, it was very accurate but that's also out of the hand of a national champion.

Or find a model 952. This twist rate discussion made me want to find out what the twist rate really is for that pistol. S&W only lists it as "special". I guess it is special at 1/18. That explains why I can get away with reduced loads and still get good performance. You won't save any money picking one of them up but you will (with practice) get smaller groups.

Len

OldMaster64 wrote:Or find a model 952. This twist rate discussion made me want to find out what the twist rate really is for that pistol. S&W only lists it as "special". I guess it is special at 1/18. That explains why I can get away with reduced loads and still get good performance. You won't save any money picking one of them up but you will (with practice) get smaller groups.

Len

A 952 is my list of wants but not many have fallen under my radar for sale.  Maybe someday.

No more excuses Beezer

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=466786351