Velocity Loss from reduced barrel length???
Old Sneaky Pete here: A question just poped into my head and I would guess that someone could give me a good "Ball-Park" answer here. IF my MV is 3150 +/-15fps and I'm shooting a 24"match bbl. WHAT would my MV be if that match bbl was majically reduced to 16" firing that same bullet under the same conditions??? I don't knw where this stuf comes from--just sitting there and pop another thought. THANX--SNEAKY
kinda depends on the cartridge and the powder...is it done burning /max presssure at 16 ?? then not a big diff, but if not...and you need all the bbl to complete the burn...big diff...
need more data the load, cartridge,powder......oal...
mike in co
Old S/P here: Sorry about not supplying necessary data. Cartridge= .224 Hornady 55gr V-max moly, LC cases, Win S/R primers, IMR 4895 25.5gr+/-0.1gr, OAL 2.248+/-0.001. MV@ +10' =3150+/-15fps. I use moly in the bore also--a 24" JP Enterprises match bbl. I hope that this is satisfactory info. THANX--S/P
Last edited by sneaky pete; 10-05-2008 at 07:18 PM.
Years ago, a friend dropped a patch in his bore & bulged it at 11" when he shot it out. His gunsmith backbored the barrel past the bulge & crowned it somehow & the little tube still shot up with the rest of the guns on the bench.
Still, that was back in the seventies before everybody replaced waiting out with horsepower.....
sneakypete: A year or 2 ago, Jason Baney, on the "accurateshooter" website did a test, chronographing, and cutting 1" off the barrel, chrono, cut 1", etc. The general loss he came up with was approx. 8 fps for each 1" of cut-off. Don't remember the cartridge he tested with, but I was surprised: thought the fps loss would have been higher.
20 years ago a customer wanted to shorten his Rem. 722 in .222 Rem. from 24 in. to 20 in.
In this I saw a golden opportunity to test the old 50 feet per second loss of velocity for each inch of barrel removed, boy was I surprised.
He shot BL-C2 and the loss in velocity was virtually non existant between the 24 inch before and the 20 inch after barrel.
Originally Posted by sneaky pete
I GUESS THE LAKE CITY CASES MEANS THIS IS A 223 ?
SO WITH SOME ADJUSTING TO GET YOUR KNOWN VELOCITY AT 24" , 20" SHOWS 3015.....16 IS 2838 , IN NEITHER CASE IS COMBUSTION COMPLETE WHEN THE BULLET LEAVES THE BBL.
I TRIED 2 OTHER POWDERS, they all showed the same drop...so it may be built into the quickload software.
i just ran sie 80 at 2.450 with a max load of varget at 2900 with 24" goes to 2794 at 20.....at 16..1700
Last edited by mike in co; 10-05-2008 at 11:41 PM.
There are a LOT of generalities popping up on this thread. For example, best I can remember, the JB test referred to was a 6 BR, & the barrel started at 30 inches. "Efficient" cases like this, including the PPC, burn relatively fast powders, and don't lose much when the barrel is shortened. On the other hand, a .270 Winchester, a .300 Weatherby, etc., that use slower powders, lose a fair bit going to 20 inches from 24, or even 24 from 26 inches. Even with these chamberings, the loss is less (I believe), if you chopped a 32-inch barrel down to 30.
old Sneaky Pete here: Thanks again for all who offered info. I ran some of the ballistics parameters on JBM ballistics and got a good idea on what kind of varitions the drop( shorter length) Could give at impact. THANX--S/P
As muzzle energy goes down from shrorter muzzle length, the unused propellant energy goes to more muzzle blast. Personally I find that muzzle presures over 10,000 psi arevery unpleasant especially if they're under 20 inches from my head. Unless everything is perfeclty symetrical high muzzle pressure can hurt accuracy.
How 'bout sum real world numbers.
All cut with a PT&G reamer, zero freebore, .250 neck, 46 clicks AA-2230, 40gr. moly plated Noslers.
Three Rock 26" barrels, average velocities of 3797, 3829, & 3770.
One 18" Rock on a X-P 100, average velocity 3520.
Different barrels, different days, different temperatures, probably safe assumptions.
Lyman reloading manual gives estimates
I seem to remember the estimates were broken down into velocity ranges. I think at your velocities they estimated 25 fps per barrel inch. So cutting eight inches off may result in 200 fps slower. Maybe if you go to a faster buring powder some of that could be offset.
Originally Posted by alf
the variation in the three bbls is more than the per inch drop...
just my opinion...
lighter bullets and longer bbl
mike in co
Another example why I don't like to post.
Originally Posted by mike in co
DIFFERENT BARRELS, DIFFERENT DAYS and DIFFERENT TEMPERATURES !!!
72 to 85 DEGREES !!!
Average out the 3 to 3800fps to the 1 at 3520 gives you 46 fps per inch loss.
Real world, not off the damn computer.
If you don't think it' right, chamber up four of your own and get back to us.
i am not yelling or screaming at you........
he is shooting 55's at 3150 from a 24, you are shooting 40's from a 26....apples and oranges........
he claims plus or minus 15 fps, your 3 bbls have a plus 29 minus 30...twice his window....appples and oranges.
your showing an average on three bbls of 46 fps/in, the lovely computer , tuned to HIS data shows 39fps/in. the real issue is you are shooting a much lighter bullet. bullet weight means more burn time per inch of bbl, so it does matter.
for the record i have multiple 223's from 17.5 to 26 inch bbls, but no bbls from the same maker, and i do not shoot the same load in any of them....so no useable data for this example.
your allowed to have an opinion and i am not allowed one?
be an adult.
mike in co