The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading what make one barrel slower than anotherGo | New | Find | Notify | Tools | Reply | |
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| One of Us |
This is the 4th older winchester model 70 I have worked up loads for and it runs 200-250 fps slower than what the books say. Accuracy ok, but basically it's a 308 win as to velocity. this has been the case with 2 pre 64s and two post 64s 2-7mm rem mag 1-30-06 1 338 win mag not worried to max out the velocity, just curious as to the cause? | ||
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A plethora of factors can influence the velocity you get from one barrel versus another. The chamber dimensions can effectively make for a larger pressure vessel, therefore less total pressure resulting in less velocity. The throat can be longer (more "freebore") resulting in much the same thing as an overly generous chamber. Bores can be tighter or looser. Bores can also be smoother or rougher. And the type of rifling can influence velocity. Finally, chronographs, especially the earlier and inexpensive ones, can consistently provide lower or higher readings than the actual velocity, usually a result of screen spacing error. With those using just a 12" spacing like the little folding Chrony, tilting the body of the machine so that the bullet travels between the screens at an angle can skew the velocity significantly slower than the actual velocity simply because the bullet travels more than 12 inches between the screen detectors. For instance, if the effective distance between the screens is 12.6", then that represents a 5% error on the slow side. Five percent of 3000 fps is 150 fps, or about the amount slower you're finding your velocities. Any or all of the above could be in play. | |||
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Stonecreek covered a lot of the basis. The one time I had the problem it was a ridiculously long throat. | |||
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You can also have two identical barrels produce different velocities. It's sorcery because there is no explanation for it. If the throat is longer, or bore is tighter, then they aren't the same barrel in the first place, and the differences explain it. | |||
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Just the Gun Gods foolin' with ya'. NRA Benefactor Member US Navy Veteran | |||
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Thanks, all stuff I had considered but one never knows when they'll get some new information. bottom line is it shoots just under 1' with several bullets and two different powders so everybody happy  | |||
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| Administrator |
Shot 5 Mannlicher rifles in 270 Winchester. All identical, brand new. With the same ammo. Norma 150 grain. Velocity difference between then was over 150 fps?? | |||
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bore too small or bullet too big. Don't over think it and a few other none important thang like roughness, pits and blockage.. Ray Atkinson Atkinson Hunting Adventures 10 Ward Lane, Filer, Idaho, 83328 208-731-4120 rayatkinsonhunting@gmail.com | |||
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Bad JU JU. | |||
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It's magic. I had two identical Krieger barrels, chambered with the same reamer by the same gunsmith on the same lathe and they had over 100 fps difference with identical loads. They both liked the same load, seated the same distance from the lands but still showed that velocity difference. Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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Book values? Mostly marketing hype. Testing often done with long barrels especially set up to get target velocities. As noted, a lot of variability under normal circumstances too.
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I shoot two .358 STA's, both custom rifles, one from Winchesters custom shop and the other with a Lilja barrel. Both are Model 70 actions the Lilja action post 64 the Winchester pre 64. The Lilja barrel shoots from 50 to 100 fps faster on all size bullets. I cannot chamber the brass shot through the Winchester barrel then resized in the Lilja barrel. This tells me the chamber sizes are different. Am I wrong in thinking the difference in speeds are a result in the difference in chamber sizes. Both rifles are super accurate capable of ragged hole three shot groups when the shooter does his job. Good Shooting. phurley | |||
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Yes. It would take much more variation in chamber size than just normal allowable tolerances, to make that much difference in velocity. Was stated above, it is something else. I your case, it is different barrels. And it also might be the chamber throats, bore size, and lengths. Comparing apples to tomatoes. Both are red but the similarity ends there. | |||
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i personally believe, along with all the voodoo, that it's friction and diameters - a MINOR case difference isn't going to remove all that much energy but i could be entirely wrong #dumptrump opinions vary band of bubbas and STC hunting Club Information on Ammoguide about the416AR, 458AR, 470AR, 500AR What is an AR round? Case Drawings 416-458-470AR and 500AR. 476AR, http://www.weaponsmith.com | |||
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Yes, friction and diameters from completely different barrels; different manufacturing method, rifling configuration, and who knows what the dimensions are. Chamber dimensions; no, except for throat diameter and length, possibly. Speaking only of the two different rifles that P5 has. | |||
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I shoot four Model 70 Winchesters rifles in .270 WSM and have for years. I load them all for my family and friends and have extensive records of all shots fired and chonographed.One is a stainless all weather model and shoots all bullets faster than the other three blue barreled rifles. It shoots the 130 grain Northfork bullet 3450 fps while the others shoot it 3350 fps same load. It shoots other buillets faster also with same loads. Just saying all barrels are unique unto themselves. Good Shooting. phurley | |||
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I owned 5 Ruger 44mag pistols. Four 7.5 barrels one 5.5 Then 5.5 is faster the the 7.5s. | |||
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I have an old 03 springfield that still had the original two grove rifling, chronographed 200-300 fs slower than average. I gave it a new barrel, woke it right up. Tightened up the groups too! I also have an old National Arms 06 built on a 98 action that chronographs on the heels of a 300 WM for some weird reason. Small variations in the barrels, some can be explained, others cannot. | |||
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Some forget reloading data from the books is done inside, at see level, and most likely at room temperature, with their rifles or launching device. All of those factors don't exist in the field. Rarely have I worked up a load that matched a published velocity. In most cases my loads are faster. I live at 4000 feet and hunt in elevations from 4500 to 8500. | |||
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200 to 250 FPS is a bit extreme, Id change barrel makers in most cases. I've use Lothar Walther for umpteen jillen years and never had a barrel deviate more than 30 or 40 FPS. ???????not saying! Ray Atkinson Atkinson Hunting Adventures 10 Ward Lane, Filer, Idaho, 83328 208-731-4120 rayatkinsonhunting@gmail.com | |||
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