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Thread: what do you make of this?

  1. #1

    Default what do you make of this?

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    so this weekend i decided to test how putting a crimp (using a factory crimp die) affects my bullets. this is on a 338 win mag savage, benchrest at 100yds. this gun has an adjustable muzzle brake which i also tested if it affected accuracy open vs. closed. everything has the same amounts of the same powder, same brass, all 0.020" off the lands, and same primers. several fouler shots were taken. all were 3 round groupings except i did have an extra heavy crimp bullet so thats a 4 round group.
    upper left: heavier crimp
    bottom left: moderate crimp (i do remember "pulling" the bullet that hit center)
    bottom right: light crimp (1 outlying round was a fouler shot)
    center: 1 barnes factory round and 3 no crimp
    upper right: no crimp - open muzzle brake
    all shots except upper right were with a closed muzzle brake. at least 1 minute was taken between shots with the bolt open to allow for some barrel cooling. unfortunately i don't have access to a chronograph so all references to velocity will be based on if it hit high or low on the target.
    it seems as though i may have gained a slight amt of velocity with mod-heavier crimping but at a loss to accuracy. i really expected to gain accuracy with crimping. a light crimp still had accuracy but similar point of impact as no crimp and closed muzzle brake. here's where i'm really scratching my head...when i opened my muzzle brake i had a completely different point of impact compared to when the same bullets were shot with a closed muzzle brake. i'm guessing that has to do with barrel harmonics but at 100 yards should i really be seeing that much difference (basically 1 inch of windage and 2 inches of elevation)?
    my take away from this weekend is that i'm not going to crimp and will shoot with a closed muzzle brake all the time.

  2. #2
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    Quote Originally Posted by ak-fang View Post
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    so this weekend i decided to test how putting a crimp (using a factory crimp die) affects my bullets. this is on a 338 win mag savage, benchrest at 100yds. this gun has an adjustable muzzle brake which i also tested if it affected accuracy open vs. closed. everything has the same amounts of the same powder, same brass, all 0.020" off the lands, and same primers. several fouler shots were taken. all were 3 round groupings except i did have an extra heavy crimp bullet so thats a 4 round group.
    upper left: heavier crimp
    bottom left: moderate crimp (i do remember "pulling" the bullet that hit center)
    bottom right: light crimp (1 outlying round was a fouler shot)
    center: 1 barnes factory round and 3 no crimp
    upper right: no crimp - open muzzle brake
    all shots except upper right were with a closed muzzle brake. at least 1 minute was taken between shots with the bolt open to allow for some barrel cooling. unfortunately i don't have access to a chronograph so all references to velocity will be based on if it hit high or low on the target.
    it seems as though i may have gained a slight amt of velocity with mod-heavier crimping but at a loss to accuracy. i really expected to gain accuracy with crimping. a light crimp still had accuracy but similar point of impact as no crimp and closed muzzle brake. here's where i'm really scratching my head...when i opened my muzzle brake i had a completely different point of impact compared to when the same bullets were shot with a closed muzzle brake. i'm guessing that has to do with barrel harmonics but at 100 yards should i really be seeing that much difference (basically 1 inch of windage and 2 inches of elevation)?
    my take away from this weekend is that i'm not going to crimp and will shoot with a closed muzzle brake all the time.
    I think,
    that your tests should not be considered conclusive, due to the small amount of testing.

    You might get the same variation if they were all fired with the same crimp, and/or with the brake on or off.

    SOTN

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  3. #3
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    None of that shooting really sucks. So, you are splitting hairs really. With not much work, I am sure you can tighten those groups up. Nice job so far.

    3 shots is statistically difficulty to make a conclusion, especially when you pull one so it is a sample size of 2. Shoot 2 or 3 strings at the same place, and only change one variable and then see what happens. You could do no crimp, a heavy and a light crimp for three groups. 3-4 shots each string with 6 strings is 18-24 shots. Should take you around an hour if you shoot in the winter when cooling the barrel is easier. Shoot two strings at each bulls eye. You will see a definite pattern emerge after the 4th or 5th shot . Also, try to limit the variables of how you shoot. That is why a lot of load development is done off a lead sled. The break should be the same for all the tests. It usually changes the POI if it is on or off. The accuracy will likely be the same with it on or off.

    Preliminary data from your posted test would suggest a change based on point of impact differences from more center vs to the left. So the crimping is doing something.

    The crimp should gain a more consistent starting pressure and reduce your velocity spread and thus improve accuracy. So, you really need a chrony to see if the crimp is doing what it should. Without the crony, you are relying on accuracy of your shot alone to determine the best load. There are a lot of variable to control during the shot that do not effect what happens at the chrony making it a nice tool to confirm what you are seeing on paper.

    I don't always use it because all I am really after is a consisted load about one MOA that I can shoot to 300 yards. Most of my guns have that without really worrying about the little differences to make the load a .75 MOA or .5 MOA. I have two guns that are more long range affairs, 400-600 yards. Those I like to get the chrony out for, but I have not for a couple of years now.

    So, what is your goal in all of this?

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    Another vote for not enough testing to be conclusive. I'd also venture if you picked one type of ammo and one setting the brake you'd see almost the same variation group to group than by changing settings.

    On more than one occasion I've shot a 1/2" 3 shot group during load work and figured that was go to load and proceeded to load up a box or two of that ammo. Then before hunting season I go to the range to double check my zero and find my groups have opened up to 1/2". I'll go back to the range again and find the same ammo is grouping 1/2".
    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

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    I'm with the rest of the posters. More groups should be shot to verify what is really happening. I've been shooting muzzle braked rifles exclusively since around 1991 and they do shoot to a different point of impact with the brake on vs off. Only your rifle can tell you what the difference will be.

    I don't crimp rifle rounds because it adds another variable to the equation. Your case neck tension already varies a little bit from round to round due to the difference in case neck length and the elasticity of the brass. This variation will influence pressure and velocity to some degree. Since the brass varies in length and has varying degrees of elasticity from case to case, I doubt each one will respond the same to x lbs of crimp. Some rounds will crimp where they are supposed to and others will crimp less because of the properties of the brass.

    I realize a lot of factory ammo and military ammo is crimped but I'm not convinced it makes a difference in accuracy. If someone else has some scientifically verifiable data to the contrary it would be interesting to read.

    Another potential problem with crimping is if it is done too much you will deform the bullet jacket and I don't believe that will help accuracy either. At least it doesn't when shooting bullets from a revolver.

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    I have played with crimping rifle bullets. As expected, the results are varied. Some loads, the accuracy greatly improved. Some it was worse. One increased pressure, while another one helped to alleviate a pressure problem. So, my experience has been to use the lee factory crimp die on a moderate to low crimp and then run an experiment. I usually do not crimp loads I am working up, just because it is another variable I need to sort out. If I get a load that works pretty good, I may decrease the charge a bit (sometimes not) then shoot a few strings working up the powder charge and see what my accuracy and pressure does. So ya, it is a crap shoot. Sometimes a bust, sometimes a winner. Other times, no change.

    On a side note, there are some schools of thought on not crimping anything without a crimp groove. I use mostly Barnes bullets with the rings cut in them. They act as kind of a crimp groove. Also used them on Etips without the groove and that is one bullet that the pressure signs decreased in a 300 RUM after crimping (go figure). The crimp die says on the package it can be used on bullets without a groove, except one manufacturer's bullets that I forget right now.

  7. #7

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    Quote Originally Posted by Daved View Post
    On a side note, there are some schools of thought on not crimping anything without a crimp groove. I use mostly Barnes bullets with the rings cut in them. They act as kind of a crimp groove. Also used them on Etips without the groove and that is one bullet that the pressure signs decreased in a 300 RUM after crimping (go figure). The crimp die says on the package it can be used on bullets without a groove, except one manufacturer's bullets that I forget right now.
    thanks for the replies and i'll definitely be heading out to put more holes in paper to add a little more statistical significance. to reply your earlier post daved, with lack of access to a chrony and a lead sled i'm having to do this a little willy-nilly and as scientific as i can. i definitely understand the largest variable in all of this is not controlled for and that's me as the shooter. either way i'm having fun doing it!
    a note on the crimping; i am using the lee factory crimp die which says it can crimp on bullets with or without crimping grooves. i'm using 225 gr barnes ttsx bt bullets and the cannelure lines right up with where i placed the crimp.
    i would be very interested on people's thoughts on neck tension. my thinking was the crimping would be making the neck tension a little more uniform...am i off-base with that?

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    With case necks we really have at least three problems. Unequal lengths, unequal thickness and differences in brass elasticity.

    You can fix length by trimming cases to a uniform length. I usually do so to within .002 but with care you can do better.

    Case thickness can be mitigated by turning case necks. I've never tried that myself nor have I tried inside reaming of case necks. I once read inside neck reaming won't fix the problem because the cutter follows the path of least resistance. Meaning, if your case is thicker on one side to start with, it will stay thicker on that side even after inside neck reaming. Outside neck turning might be a different story?

    What I do with all my rifle brass is use a Sinclair neck sorting tool/gauge and toss any cases with more than .003 variation. You only have to measure the brass one time and this reduces the neck thickness variable to some degree. Sinclair states in their instructions "Most good shooting rifles will be able to distinguish variances exceeding .003."

    Lastly, brass elasticity can be helped along by annealing cases after a couple firings. I anneal after every two firings and I can feel the difference in resistance when seating bullets between annealed and unannealed cases. I don't know what more can be done about brass elasticity aside from keeping your cases segregated by lot. Presumably, brass varies by lot. So, keeping lots separated may also help with consistency.

    Honestly, I have no idea how much of a difference all this makes. I do a lot of this stuff and more because I enjoy it.

    A few additional random thoughts on this subject. First, John Barsness has written several articles on accuracy, handloading and brass. His experiences are worth checking out. The articles are titled Factors in Accuracy I and II, Rifle Brass, Seating Bullets Straightly, Resizing Rifle Cases: Doing it Well Can Boost Accuracy. You can Google his name and the titles to find the articles. They are worth reading.

    I've been handloading for the 338 WM since the late 1990s. While I use a lot of different tools and techniques to improve accuracy, one load has shot submoa in three of three 338 WMs I own. It is the max load from the Barnes manual #4 and as they recommend, bullets should be seated 50 thousandths from the lands and only experiment with other seating depths if needed. There are several tools available to determine where your lands begin and IMHO all seated bullets should be measured by using a tool which measures from the ogive of the bullet and not from the bullet tip to assure uniformity. I can easily seat all bullets to within .002 of each other using a micrometer adjustable seating die and measuring the bullets from the ogive.

    The load mentioned above is 67.5 grains of IMR 4350 using a 225 grain TTSX. This would be the first load I would try in any 338 WM because it has worked so well for me.

    One parting shot, factory ammo these days is really, really good. If you want to load ammo better than the factories, then pick up a box of premium rifle ammo and measure it. You will find you can improve upon the factory ammo in several ways if you're interested in doing so.

    Hope this info helps.

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