http://precisionrifleblog.com/2012/0...y-reliability/
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As you said "I can't figure that one out", something else wonky is going on.Quote:
Originally Posted by seabast
What was the spread of velocity that you had? How round were the holes in the target? If you are losing 800fps and that is a legit number then something weird is going on. Have you verified the diameter of the bullet? Do you have a beam scale and a digital scale, or 2 beam scales to double check the charge weight against one another? Something is just not right here.
You are correct Fox, going from a barrel length of 24" to a 22" barrel will not account for a loss of 800fps.
I have loaded for 3 .243's with 22, 24 and 26" barrels. With same load data there was at most a 100fps difference between the 22" and the 26". Powders used are imr4350, H4350, H4895 and H4831sc. I currently load a 24" barrel for 87 and 100 grain projectiles, IMR4350 for both applications and speed values are close to published data.
Anyways, just to reiterate, 2" of barrel length is not responsible for that loss of speed
No it's a combo of things for sure but slower burning powders don't work well with shorter barrels.Quote:
Originally Posted by Fox
No it won't necessarily burn it all up in the first 18 inches either.
So yeah 2 inches plus a few other factors will result in crappy MV's
Velocity "Loss or Gain " , from Chuck Hawks site.
Of interest is the last paragraph.
Velocity loss (or gain)
It is worth noting that the velocity figures published in ammunition brochures and reloading manuals are sometimes taken in barrels different in length from those supplied on many rifles. I have seen various estimates of how much velocity is lost (or gained) when a barrel is not the same length as the test barrel in which a cartridge was chronographed. Here are some of them.
The 2001 Edition of the Shooter's Bible states, in the introduction to the Centerfire Rifle Ballistics section, "Barrel length affects velocity, and at various rates depending on the load. As a rule, figure 50 fps per inch of barrel, plus or minus, if your barrel is longer or shorter than 22 inches." However, they do not say what category of load to which this 50 fps average pertains.
Jack O'Connor wrote in The Rifle Book that, "The barrel shorter than standard has a velocity loss which averages about 25 foot-seconds for every inch cut off the barrel. Likewise, there is a velocity gain with a longer barrel." He went on to illustrate this using a .30-06 rifle shooting 180 grain bullets as an example, so his estimate was obviously for rifles in that general performance class.
Other authorities have tried to take into account the different velocity ranges within which modern cartridges operate. The Remington Catalog 2003 includes a "Centerfire Rifle Velocity Vs. Barrel Length" table that shows the following velocity changes for barrels shorter or longer than the test barrel length:
MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.
The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length and agree with the Remington figures. The Lyman table shows the following approximate velocity changes:
For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.
The 43rd edition of the Lyman reloading Handbook gave some concrete examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26 inches down to 22 inches with the following results:
The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.
For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24 inches down to 20 inches with the following results:
The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.
After a bunch of disclaimers, the Lyman people concluded, "The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types." It's funny, but that is what I had suspected all along!
Lol what about high speed large bores....
I know with my custom smokeless muzzleloader with same load and bullet I saw a 160 fps lift in mv when going from a 26 to 28" barrel. 2505 to 2668 respectively with a 300 grain pill
But with a different bullet but same weight that difference was close to 100 feet per second difference using same powder charge....
Working with those has taught me not to make assumptions....
It all comes down to the fact that in his rifle that load stinks. If he has put the load together right there is nothing more to talk about as that is the MV for that load out of his rifle. Your 243 might act different with that load but that doesn't mean there is anything wrong with his rifle.
I'll go one further, I have seen identical Caliber rifles produce a spread of 300 fps + on same loads to Sami spec. Same range session and same batch yet individually ES was under 30....
That's why we handload. It is to tailor loads to our rifle.
Go with a better powder suited to his rifle.
I am still not convinced it was caused by barrel length or powder choice. I believe your chronograph setup was the problem. Too much sunlight or lack off can give you funky readings. Google it or read the link I posted previously.
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It has always been said, each and every rifle is different, as you have stated, " That's why we handload. It is to tailor loads to our rifle. "
My buddy and I bought two identical rifles years ago, Winchester model 70's both in .243 cal. his was faster by close to 280 fps. , till I wore out my barrel and had it re barreled with a Shilen Match Grade Barrel and a tight chamber was cut, now mine is faster than his by between 60 to 72 fps. on my Oehler Chrono.
Go figure, as has been mentioned, there are too many variables.
The first paragraph of my post above explains a lot, the loading manuals give you velocities that they/the companies got out of their barrels, that is not necessarily what you will get out of yours.
It is worth noting that the velocity figures published in ammunition brochures and reloading manuals are sometimes taken in barrels different in length from those supplied on many rifles. I have seen various estimates of how much velocity is lost (or gained) when a barrel is not the same length as the test barrel in which a cartridge was chronographed. Here are some of them.
One thing that I notice here a lot of ,is that many newcomers to reloading ask " what is your favorite load for such and such ".
One thing that I never do is state what loads I use in my rifles of any particular caliber because, "What is safe in my rifle , may be dangerous in yours ".
Of particular note, One fellow last year was on here saying I am just getting into reloading and bought such and such equipment, about a month later he was on here giving out advise on particular loads to others, which made me shake my head in disbelief.
This reminds me of a cartoon with a goofy looking guy, the caption said " six munts ago I kudn,t evun spell unjinear, now i are one ".
Just to validate much of what the experienced here have already posted AND to throw in an alternate observation which, I suppose, still validates individual barrel characteristics.....
Our department's Tango 51 builder(TacOps) did some specific testing on a .308 win barrel that was cut one inch at a time from 26" down to 22" with little change in fps. They basically cut 1" and shot ~20 rounds of Federal Factory 168gr Gold Medal Match ammo to document MV FPS. They then removed another 1" and shot 20 more rounds and repeated down to 18".
The biggest change in MV FPS that they documented was the reduction from 20" to 18" on their barrel and it was 32 FPS if I recall correctly even with or without the can.
We opted for the 18" and both had a consistent 2630 MV within ~ 5-10 fps and shot less than 1/4" at 100yd with or without the can installed. It had a 3 MOA deviation in POI from can on, to can off, yet still grouped less than 1/4".
I am interested in hearing the final poop on what specifically was found to cause a 800 fps delta.
I always shoot with my screens installed unless I use Big Jack's LabRadar but I like to loophole practice when at the farm and the screens define my loophole.
I usually get consistent MV or and error code.
Quote:
Originally Posted by seabast
In the .243 Win. I prefer to use IMR 4064. Having said that it may be possible that the barrel on your .243 may have a different twist ratio then the gun used to establish the velocities in the manual, The variation in the twist ratio can result in a slow or fast barrel, which affects muzzle velocity. Projectile with longer bearing walls tend to give better performance in rifles with a fast twist, whereas projectile with short bearing wall give better performance in firearms with a slow twist. That aside, why is it important to match manual ballistics? In my mind, the important think is to find a load that gives consistent performance in your particular firearm, regardless of velocity. Actually lower velocity bullet that provide for consisted performance, will extend the barrel life of your firearm. Just some thoughts.
You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut