Speed question

J

jaybic

Guest
Hello, yet another question from the peanut gallery.

A buddy and I tested his hand load(34.5 gr H4895, 50gr vmax, win cases and CCI br primers) in his rifle which is a Rem 700 lvsf in 22-250. His rifle gets 3621fps(5 shot avg) when seated .20 off his rifling. I then tried 5 of his hand loads in my Savage 16 Weather Warrior seated .20 off my rifling and the 5 shot average using them in my rifle was 3784fps. That is 163fps difference. We then tried my go-to load of 36.5gr of varget(same brass, primer and bullet) and my rifle averaged 3746fps and his rifle averaged 3525fps using my load. That difference is 221fps.

Both have 22 inch barrels but his is 1:14 twist and mine is 1:12. I realize that chamber dimensions or perhaps headspace(this starts to get beyond my scope of knowledge here) may have something to do with this but I am hoping maybe some of you guys can point us in the right direction here. We are trying to get a 50gr bullet going 3700 fps(anything over is a bonus with a 22in tube for us) and even using a book max charge of Varget, can only get it going 3525fps. Is his chamber sloppy or mine too tight or ????

Maybe thats just how it is and we should stop fishing for something we cant fix.

Thanks,

Jamie
 
In several 22-250/22-250AI's, absolute best accuracy/highest velocity shooting 50's is with Reloder 15. My barrels are 14" twist. And two different barrels can also have a pretty substantial velocity difference. I have 4 -.223AI barrels chambered with the same reamer and having the same twist. With the exact same load there's 200fps difference between the fastest and slowest.
 
Each barrel tends to be different. I have had match barrels that act similar but few are exactly the same. Factory barrels vary a lot. Other things being equal a rifle barrel with a tighter bore will shoot faster than a looser bore.

With the short 22" barrels and the large case volume in the 22-250 a faster powder may work better. I usually use 28 or 29 inch barrels for my 22-250 AI applications. The longer barrel get the velocity with much lower muzzle pressure. (Muzzle blast destabilizes the bullet.)

Usually I have found with the correct powder and load I can get faster velocity with the slower twist barrels.

I am usually more interested in precision than speed but shooting in hard to read wind conditions speed does help.

My 222 with a 1-14 twist barrel gets 3,850 with the Moly coated Berger 30 gr FBHP bullets using H-4891 powder. It is also fast with the 40 gr Moly coated V Max bullet. I load with the bullets into the lands about 0.005". With boat bullets I have been in first place at the end of the day at our small club matches when the wind was blowing tricky and others were shooting the 6 PPC.
 
IMO taking good readings and good notes, finding out what IS, is more important than "fixing it."
 
Jamie I am using 39G of IMR 4895 and getting right at 4000 fps with a 50G Hornady Vmax in my 22-250AI . accuracy is in the high 2s with 5 shot groups. My barrel is a 23" Lilja 3 grove.
 
Jamie a 12 twist will build pressure faster than a 14 twist and you may be seeing some of those effects. I wouldn't go so far as to say ALL the extra velocity is because of this but SOME is.
 
Roger T said:
Jamie a 12 twist will build pressure faster than a 14 twist and you may be seeing some of those effects. I wouldn't go so far as to say ALL the extra velocity is because of this but SOME is.
Click to expand...

Roger have you tested this? I haven't found it to be true.

al
 
In theory a tighter twist will build pressure faster than a slower twist other things being equal. On a barrel to barrel comparison the difference between 12 and 14 may be to slight to see. Minor variations in barrel ID show up quick. How the bullet enters the barrel can make a difference. And so on...........
 
Alinwa, My (limited)tests were done on 6-250s (10tw -8tw)and 308s (12tw-10tw)2 rifles ea cal (LIMITED) as I said. All 4 were Smithed by the same Smith (each caliber was done at the same time). Specs were the same EXCEPT twist with each cal. The 8tw 6-250 MAXED 1.2grs. less with 95gr bullets (Noslers)with a 47fps higher vel. The 308 10tw was not as dramatic but still maxed with a lower charge (.4 gr. less) with 28 fps higher vel. Scientific proof (I'm not an engineer) but that has been my experiance.
 
Lotta' 'might's' and theories and maybe even conflicts here :)

I think what you're saying Roger is that in your experience a faster twist barrel gives greater velocity?

My guess is that Octopus's theory allows for the exact opposite......??... or does the theory allow that "building pressure faster" somehow increases velocity? AND imparts additional rotational energy???

Seems like free energy to me.

al
 
Al, Using the 6-250 as the sample. How would you explain the lower charge/Max pressure with the faster twist ? If I'm all wet throw me a towel :eek:. The difference in charge weight (to me anyway ) seems a bit drastic for having the same chambers/throats/freebore and leade. The cases can/have been used in either rifle.
 
In theory a tighter twist will build pressure faster than a slower twist other things being equal. On a barrel to barrel comparison the difference between 12 and 14 may be to slight to see. Minor variations in barrel ID show up quick. How the bullet enters the barrel can make a difference. And so on...........

A little confusing here. Likely my fault. If you shoot two equal rounds in two equal barrels with the only difference being the twist. The 12 twist with more barrel drag would build more pressure and be slightly faster.

However, If you load to the exact same pressure the 14 twist would be faster as it has slightly less drag. With slower twist you can use more powder and get to higher velocity with the same pressure curve.

Likewise, If you load with moly or similar lubrication on the bullet you can can use more powder and get to higher velocity with the same pressure curve.

When smokeless powder is contained it will build higher pressures. That is the way it works.

Maybe one of the members with more rocket science will explain this better.
 
I'm no rocket scientist and can't 'explain' anything but here's what I've experienced.....

-The real scientists (including Harold Vaugh, a rocket scientist ;) ) put bore friction so far down in the dirt as to be immeasurable and the effect of twist to be a tiny fraction of that.
-My own experience with maybe 20 combinations of chamber and twist are different than Rogers. I've had 6BR and .243AI's in twists 8-10-12-14 at the same time so's I could run them head to head. I've rechambered maybe 6 of these barrels, switching from 6BR to .243AI or visey varsey. Some are definitely "faster" than others but independent of twist rate. I'm not sure why altho Octopus may be onto it with the barrel id thing.....
-Harold Vaughn argues quite convincingly that lowered velocities experienced with moly have nothing to do with "reduced bore friction" and furthermore that IF moly actually DID reduce bore friction velocity would rise. All engineers of which I'm aware agree with this.
-"When smokeless powder is contained it will build higher pressures. That is the way it works." Well, kinda'.... yes as pressure rises the reaction quickens but the actual yield doesn't change as long as all components are consumed and "quicker" doesn't always translate to higher velocity even if it does spike to higher pressure momentarily. As an extreme example a fast burning pistol powder will destroy a rifle by producing tremendous pressure but won't ever produce high velocities no matter how you meter it. Incidentally, smokeless powder is tested by firing it in a "bomb gun" which has no exit, no barrel or bullet. This method is used to establish the total amount of energy available. Gunpowders are basically a fuel load with a contained oxidizer, yield is based on consumption of the component fuel. Final velocity is the result of how you use this fuel load. It's really no different than a drag race, two cars with equal horsepower don't necessarily run the same 1/4mi times.


And please understand, I'm not trying to convince anyone of anything :)

I just have a different opinion and am sharing it.

al
 
alinwa said:
All engineers of which I'm aware agree with this.

al
Click to expand...

That's no longer true Al. I have the degree and I don't agree with it. I've seen it even in rimfire - lower bore resistance leads to lower velocities - all else being equal. Does the twist difference in the OPs post account for ALL of the velocity difference? Probably not - but the powders and quantities used don't burn completely prior to bullet exit in most centerfires - so the one that builds, and maintains, the higher mean pressure will result in the faster bullet - and still have energy to spare after the bullet is gone.
 
Thanks vibe, now... where did you get the information that "all the powder doesn't burn on most centerfires?"

al
 
alinwa said:
Thanks vibe, now... where did you get the information that "all the powder doesn't burn on most centerfires?"

al
Click to expand...

I typed up a lengthy reply and got "Token has expired reload last frame"
Let's just start with one that you think does not.
 
Vibe said:
I typed up a lengthy reply and got "Token has expired reload last frame"
Let's just start with one that you think does not.
Click to expand...

I have no reason to believe this to be true of ANY round I use..... From 6PPC to 300WSM, even 338 Lapua, I'm able to achieve consistently small ES figures. If your contention is true then I must be blowing the exact same number of unburnt kernels downrange, or the bullets must be exiting at the exact same time in the burn cycle with each firing. Dude I must have some good primers.

IMO your logic is akin to asserting that "gasoline engines are only 20% efficient" etc etc.... of course followed by "my yuncle Bill made a carburetor and the feds fed him to the fishes..."

Does it follow then that "the gub'mint and the powder companies are suppressing the good stuff?"

LOL

al
 
alinwa said:
I have no reason to believe this to be true of ANY round I use..... From 6PPC to 300WSM, even 338 Lapua, I'm able to achieve consistently small ES figures. If your contention is true then I must be blowing the exact same number of unburnt kernels downrange, or the bullets must be exiting at the exact same time in the burn cycle with each firing. Dude I must have some good primers.

al
Click to expand...
Actually, no, your example does not logically follow. Neither does your primary example, though in a crude form it is basically correct. A consistent load of a consistent powder will give consistent results - even if a component of those results is that some of the powder is still combusting at the time of exit. A given caliber, using molly coated bullets, will require a larger amount of powder to achieve the same muzzle velocity - because the powder reacts more efficiently and/or completely while at the higher pressure. the bore friction keeps that burn efficiency high - the higher the resistance to expansion, the more complete the burn. Which is all well and good if your goal is to burn powder completely. Ours usually isn't - our goal is consistent muzzle velocity (behind an ever increasingly departing bullet - which tends to drop pressure rapidly even before the bullet is gone) - so we throw more of a slower burning powder behind it to keep that pressure high longer. The result is the desired muzzle velocity, at the expense of a complete burn. The side effect is large muzzle flashes from unexpanded gasses and incompletely burned powder being expelled from the muzzle. And so long as our bullets go to where they are pointed, and do it consistently - the unburned, or late burned powder consumed after the bullet is gone is of no real consequence to most shooters.
 
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