Quantcast

Why Velocity Varies Between Rifle Brands

Discussion in 'Gunsmithing and Repairs' started by jfr, Oct 11, 2018.

  1. jfr

    jfr Member

    Joined:
    Oct 8, 2018
    Messages:
    4
    I'm new to this forum, but not to guns. I have a rather perplexing question as to why certain manufacturers rifles seem to underperform and others over perform from factory specs. I have been hunting and quite successfully I might add, for the past 50 years. Recently I jumped on the bandwagon and went with a new lightweight rifle in a new razoo chambering. BTW, I began reloading more than 40 years ago, and rarely every shoot factory loads, unless economics dictates the cheapest way to shoot and acquire brass for a new project. Well this new rifle/chambering was going to save this old body about 2 pounds on those long hunts while still offering comparible performance to my elk rifle. I took extra care breaking in this new rifle, working up loads, and making sure I was happy with it before I hunted with it. Just to be upfront, I worked up loads without a chronograph. I thought I had a pretty good load going with the gun and went on an antelope hunt. Needless to say I was less than impressed with the performance. But I attributed it to bad karma. I then went on an elk hunt and was rewarded with similar results. The problem was I was putting bullets where they belonged, and animals were not going down as expected. This scenario repeated the next year, and I was thinking the bullets were the problem, I went to the manufacturer and got their take on the situation and they recommended a different bullet. In the meantime, I am super impressed with new rifle accuracy and convince several friends to invest in similar outfits. On, his brother owns a gun shop and has the same caliber but different make gun, as well as a chronograph. What he found out, our guns were consistently 3-400 fps slower than his rifle with his handloads. Just to take handloading out of the equation, I have purchased 3 boxes of different factory loads and chronod them to find out the velocity difference is consistent across the board.

    Now to recap, my new brand gun, plus two others all shoot 3-400 fps slower than the friends rifle and antoher make in the same caliber. We have all gone to the range on the same day and shot on the same ammo through 2 different chromos with similar results.

    Why?
     
  2. jdh

    jdh Member

    Joined:
    Jan 5, 2008
    Messages:
    1,025
    Slug the bores, and cast the chambers.
     
  3. jfr

    jfr Member

    Joined:
    Oct 8, 2018
    Messages:
    4
    I agree, possible chamber and bore discrepancies. However, those ailments should have symptoms associated with them. Shot cases will chamber in any of the rifles, none of the loads exhibit pressure or leak issues, and my observations would indicate all chambers are within SAAMI guidelines. One thing the poor performing guns all have in common, they all have SS barrels. Neither of the good performing rifles do. I have a hard time believing this could be the issue to this extent. A 10-13% velocity drop is a big impact. Just as a side note, A friend who runs a range in another state reported similar observations with these rifles. The issue for me, I like the rifle. It is accurate, it is light, and I can shoot it well. If a new barrel was to be put on this rifle, could I expect similar performance since I would also opt for SS on any new barrel as well.
     
  4. jmr40

    jmr40 Member

    Joined:
    May 26, 2007
    Messages:
    11,350
    Location:
    Georgia
    Differences in the tolerances in the chamber and barrel will account for some difference in velocity. Somewhere around 25-50 fps is perfectly normal, and I've seen rifles shoot 130-150 fps slower than they should. Never seen anything anywhere near 300 fps. Something is wrong with both of those barrels. Generally speaking barrels with close tolerances shoot faster. Guys who go with aftermarket target barrels tend to shoot faster than most production barrels of the same length.

    I don't think SS is the issue. I have multiple 308's and 30-06 rifles. The ones with SS barrels are the fastest in my case. Virtually all target rifles are using SS barrels.

    My SS Winchester Classic 30-06 consistently beats everything I've compared it to. It shoots everything 60-90 fps faster than my blue Remington 30-06. And beat a friends blue Remington 30-06 by nearly 150 fps. It is about 25 fps faster than the SS Winchester 30-06 FWT. All guns have 22" barrels

    I have a SS Winchester EW in 308 that is the fastest 308 I own. It tends to shoot the same ammo 20-30 fps faster than the Kimber 308, both with 22" SS barrels. My other 308's have 18" or 20" barrel in blue steel. The 18" guns run about 50 fps slower than the Winchester, and the 20" gun matches the Kimber and is only 20-30 fps slower than the 22" Winchester.

    A difference in 50 fps or less just isn't a problem. 300 fps or more is.
     
    boom boom likes this.
  5. boom boom
    • Contributing Member

    boom boom Contributing Member

    Joined:
    Sep 24, 2007
    Messages:
    2,248
    Location:
    GA
    jmr40 is correct that it isn't the stainless steel doing that.
     
  6. mjsdwash

    mjsdwash Member

    Joined:
    Jan 14, 2011
    Messages:
    997
    that is one huge difference. I have seen very similar barrels with different twist drop about half that much, like a 1 in 7 dropping a 100-150 over a similar 1 in 9. But for that much, my first thought is a problem with the crono's. How far away are the chronos?
     
  7. Blue68f100

    Blue68f100 Member

    Joined:
    May 25, 2011
    Messages:
    4,367
    Location:
    Piney Woods of East Texas
    That much difference has to be the bore. Whether it's rough, over/under size combination of both, who knows. I know that twist rate can impact some if its a more than 1" difference. Never have seen that much difference before.
     
    boom boom likes this.
  8. highlander 5

    highlander 5 Member

    Joined:
    Sep 15, 2006
    Messages:
    2,439
    Location:
    lynn,ma
    I'm no ballistics expert by any means but the adage that every firearm is a law into itself. Even with modern CNC machines it near impossible to make an exact copy of an item,then you have to figure in minor variances in the steel you're using and the list can go on for ever.
    The Speer loading manuals used to have a chapter titled "Why ballistians get gray" you might want to track that down for a read. You might want to contact the rifle's manufacturer and have them check out the rifle might be a glitch some where
     
  9. JohnKSa

    JohnKSa Moderator Staff Member

    Joined:
    Jan 1, 2003
    Messages:
    13,827
    Location:
    DFW Area
    Assuming that the barrels are all pretty much the same length, there is nothing that should make that much difference in velocity. I would expect to see velocity differences from one rifle to the next, even with identical barrel lengths. But I would expect the differences to be under 100fps for the most part. 300-400fps difference out of identical barrel lengths is just crazy.

    The one thing you left out of your story is how the various rifles performed with factory ammo relative to the factory ammunition velocity specifications. What might be going on is that your friend's brother's rifle is badly out of spec in some way that is pushing velocities much higher than they should be. The other guns are chronographing slower (but within the realm of reasonable compared to factory ammunition specs) while his is off-the-charts high.

    In other words, the ammo maker says that the muzzle velocity is 2700fps and your rifle is shooting say, 2650fps while your brother's friend's rifle is shooting 3000fps.

    If that's what is happening, then the problem is with his rifle. And it is worth keeping in mind that if velocities are that much higher than factory spec, pressures are similarly higher than they should be.
     
    boom boom likes this.
  10. jfr

    jfr Member

    Joined:
    Oct 8, 2018
    Messages:
    4

    In my first post, I talked about shooting factory ammo to try to weed out any "ammo" issues. The "slow" barrels are both 24". One fast barrel is a 26", and the other is a 24". I factored in the 26" tube and disregarded the 30-40 fps advantage it has on the 24" barrel.

    To sum it all up, we had one range day where we had 2 chronos and 5 rifles present. 3 rifles were the same brand (Brand X), all 24" tubes, all SS. The other 2 were different brands, one with a 26 inch barrel, one with a 24 inch barrel. Both were blued steel. We had 3 different brands of factory ammo, 4 different handloads, and the results were consistent. 3-400 fps velocity drop in the three brand X rifles over the other 2, even when factoring in barrel length. All loads were similar bullet weights, We did find about 130-150 fps differences between the different loads. We sent about 80 rounds of hunting rounds down range that day, all in an attempt to figure out this anomaly. What was surprising, all loads from all the rifles grouped very well, and the factory ammo across the board performed as good as or better than all but one handload. They all were statistically close to factory speeds, (within 20-30 fps of factory specs.) The one handload was about 30 fps on average faster than the average of the factory loads. ( it was, however, NOT a premium hunting bullet). The other surprising take away, the chronos were very consistent even being 2 different brands. We did not do a statistical analysis to determine if the velocities variations were the result of the chonos or shot to shot variations.
     
  11. boom boom
    • Contributing Member

    boom boom Contributing Member

    Joined:
    Sep 24, 2007
    Messages:
    2,248
    Location:
    GA
    Just out of curiosity, is there a difference in the rifling among the three stainless and the two other rifles? I am thinking otherwise that Mfg. X botched their barrels and perhaps chambers. A long throat, rough machining of the barrels, improper bore size, or overlarge chambers come to mind if the headspace is all right. Each of those will absorb energy that otherwise would send the bullet down the bore. Aside from mfg. problems, the only other thing that I could think of might be rifling differences. Czech vz24's used 8x57 mm barrels with distinctive thick lands and generate less velocity than do German k98's with their skinnier lands.
     
  12. JohnKSa

    JohnKSa Moderator Staff Member

    Joined:
    Jan 1, 2003
    Messages:
    13,827
    Location:
    DFW Area
    I saw that, but you didn't give the velocities--you still haven't.
    I'm sorry, I'm trying but I can't figure out what you're trying to say.

    If "they were all statistically close to factory speeds--within 20-30fps of factory spec" then how could 2 of the rifles be 300-400fps faster than the other 3?

    If you mean that the "slow" rifles were "statistically close to factory speeds--within 20-30fps of factory spec", then they're not "slow" rifles, the problem is with the two rifles shooting much faster than factory speeds. And they are probably operating at higher than intended pressures.

    If you mean that the "fast" rifles were "statistically close to factory speeds--within 20-30fps of factory spec", then it really does look like the other 3 rifles are shooting slow and it's time to talk to the manufacturer.

    I'm trying to get my head around this but I'm not doing a good job of parsing your meaning from your posts.

    Here's what would be very helpful in unraveling this puzzle.

    1. Slow rifle velocities with factory ammo and the velocity spec for the ammo.
    2. Fast rifle velocities with factory ammo and the velocity spec for the ammo.
     
  13. jfr

    jfr Member

    Joined:
    Oct 8, 2018
    Messages:
    4
    The two fast barrels are in the 3300 fps range, The slower barrels are in the 2700 - 2800 fps range. The 3300 fps when factoring in 26" barrels vs factory 24" tubes, is close to factory specs. The SS rifles all have 24" tubes, and are over 6 years difference in manufacturing date. Factory specs claim 3250 fps, approx. What I mean by 6 yrs difference in manufactureing date, The oldest was built before 2010, the newest was built in 2016
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice