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Posted: 11/15/2003 3:30:47 PM EDT
I am wondering if anyone has ever tested M193 ammo in gelatin in 1/7 twist barrels? The reason I ask is that I may get one of the new 1/7 twist 16" barrels that Bushmaster was to have made for us, and am unsure that M193 is still suitable with this twist.

I was under the impression that 1/7 twist is grossly overstabilized for a 55-grain projectile, and that it'd fragment way too early, like it did in the 1987 Miami shootout.

I wanted to stick with M855 or the new 77gr round, if any ever becomes available from Georgia Precision, but being able to use M193 is a bonus. I know the M193 will be a little less accurate in a 1/7 twist, but I am more concerned about too shallow of a wound cavity.

Of course, I have a ton of M193, so this worries me. :)
Link Posted: 11/15/2003 4:02:39 PM EDT
[Last Edit: 11/15/2003 4:03:04 PM EDT by Yojimbo]
The 1/7 will be just fine for XM193 or any other mil-spec 55 grain ammo. The 1/7 will not overstablize the 55 grain ammo and it will fragment just fine. As far as accuracy loss I didn't notice any with XM193 when switching to a 1/7 from my 1/9. IMHO, any accuracy loss or bullet overstabiization are so marginal that's it's a non-issue. Like you said, having the ability to move up to the heavy good stuff is why the 1/7 is gaining a lot of popularity here lately.
Link Posted: 11/15/2003 6:36:56 PM EDT
1/7 twist IS way more than you need for a 55-gr projectile, but that is not a bad thing. Twist does not have any effect on fragmentation worth noting. "FN claimed that this faster rotation also causes the SS109 to have a significantly longer path in tissue before marked yaw occurs, thus producing wounds of less severity. This is simply untrue (compare Fig. 6 with Fig. 6). Additional rotation beyond that needed to keep the bullet straight in air appears to have little or no effect on the projectile's behaviour in tissue. However, there is a situation concerning rotation rates whereby these longer 5.66mm bullets can cause increased wound severity. Shooting the SS109 or M865 bullet in the older M16A1 rifle barrel (they are not intended for use in this 7-in- 72in twist barrel, but in the newer M 16A2 1-in-7in twist) produces a bullet spin rate insufficient to stabilise the longer bullets. Such a bullet will yaw up to 70° in its path through air. Striking at this high yaw angle (essentially travelling sideways), these bullets break on contact and the marked fragmentation, acting in synergy with the temporary cavity stretch, causes a large (over 15cm) stellate wound with the loss of considerable tissue (Fackler, M.L., unpublished data, 1988)." I would only disagree with one small part of this quote, written by Fackler, which is that increased spin theoretically will increase the path in tissue before yawing. However, I trust Fackler's experiments that this amount is too small to be measured. The Miami shootout you refer to occured on April 11 1986, not 1987. You may think of 1987 because that is when the FBI convened a wound ballistic workshop to assess the bullets they were using based on that shootout. I do not know what bullets were used, but they were small caliber, high velocity handgun rounds that did not fragment. A bullet was fired at the suspects heart, but did not have adeqaute penetration to reach it. I think the man's arm was in front of his heart. Penetration was limited to under 10 inches due to the low weight of the bullet which caused it to lose velocity quickly. This is the meeting where they established the 10-12 inch penetration minimum. Accuracy loss will be much less than 0.5 MOA. Conclusion: dont worry about 1/7
Link Posted: 11/15/2003 7:56:26 PM EDT
[Last Edit: 11/15/2003 7:57:21 PM EDT by billclo]
Originally Posted By stuh505: 1/7 twist IS way more than you need for a 55-gr projectile, but that is not a bad thing. Twist does not have any effect on fragmentation worth noting. "FN claimed that this faster rotation also causes the SS109 to have a significantly longer path in tissue before marked yaw occurs, thus producing wounds of less severity. This is simply untrue (compare Fig. 6 with Fig. 6). Additional rotation beyond that needed to keep the bullet straight in air appears to have little or no effect on the projectile's behaviour in tissue. However, there is a situation concerning rotation rates whereby these longer 5.66mm bullets can cause increased wound severity. Shooting the SS109 or M865 bullet in the older M16A1 rifle barrel (they are not intended for use in this 7-in- 72in twist barrel, but in the newer M 16A2 1-in-7in twist) produces a bullet spin rate insufficient to stabilise the longer bullets. Such a bullet will yaw up to 70° in its path through air. Striking at this high yaw angle (essentially travelling sideways), these bullets break on contact and the marked fragmentation, acting in synergy with the temporary cavity stretch, causes a large (over 15cm) stellate wound with the loss of considerable tissue (Fackler, M.L., unpublished data, 1988)." I would only disagree with one small part of this quote, written by Fackler, which is that increased spin theoretically will increase the path in tissue before yawing. However, I trust Fackler's experiments that this amount is too small to be measured. The Miami shootout you refer to occured on April 11 1986, not 1987. You may think of 1987 because that is when the FBI convened a wound ballistic workshop to assess the bullets they were using based on that shootout. I do not know what bullets were used, but they were small caliber, high velocity handgun rounds that did not fragment. A bullet was fired at the suspects heart, but did not have adeqaute penetration to reach it. I think the man's arm was in front of his heart. Penetration was limited to under 10 inches due to the low weight of the bullet which caused it to lose velocity quickly. This is the meeting where they established the 10-12 inch penetration minimum. Accuracy loss will be much less than 0.5 MOA. Conclusion: dont worry about 1/7
View Quote
What I was recalling was that in that fight, several of the FBI agents were hit with 55-gr FMJ rounds from the Mini-14, and they fragmented too early (3 forearm or hand hits), and if the rounds hadn't fragmented too early, perhaps their wounds would have been more serious. I also recall this being an issue in the Waco shootout, where the Davidians were using 1 in 7 twist guns with 55-gr FMJ, and the rounds weren't penetrating wallboard/etc as well as they might have if they'd either used 1 in 9 twist or M855 ammo. Here is a link of a detailed account of the fight, FYI. http://www.firearmstactical.com/briefs7.htm
Link Posted: 11/15/2003 10:40:28 PM EDT
Billclo, I was talking about an injury to one of the suspects, which according to MacPherson, was what spurred the FBI meeting. Here is a specific description from the link you provided at Firearms Tactical: "As Platt crawled through the passenger side window, one of Dove’s 9mm bullets hit his right upper arm, just above the inside crook of the elbow. According to Dr. Anderson, the bullet passed under the bone, through the deltoid, triceps and teres major muscles, and severed the brachial arteries and veins. The bullet exited the inner side of his upper arm near the armpit, penetrated his chest between the fifth and sixth ribs, and passed almost completely through the right lung before stopping. The bullet came to a rest about an inch short of penetrating the wall of the heart." In regards to the injuries you speak of...I read the entire description of the Miami shootout, and could not find any part of it that suggested premature fragmentation in the FBI agents. The Mini-14 which the suspects used has an 18.5" barrel and thus will produce muzzle velocity around 3000 fps, like an M16. It would not be possible for this to fragment in the hand as you suggest. It would not fragment until passing at least a couple inches, more likely 3 or 4 inches. If fragmentation were to be retarded, this would cause more drastic problems. Most important is the ability to fragment in a direct torso shot. The fragmentation of the .223 is largely contained within the average torso. If the fragmentation range were to be retarded it would reduce the permanent cavity displacement to the more typical unobstructed torso shot. But I don't see any evidence to the end that twist rates would affect fragmentation range. "Additional rotation beyond that needed to keep the bullet straight in air appears to have little or no effect on the projectile's behaviour in tissue." - Martin Fackler If Fackler isn't the expert, I don't know who is. But honestly, where did you hear that the twist rate was causing fragmentation to occur sooner? No offense but it sounds like a load of bull. About the M855 fragmenting later than the M193, I do agree with that part.
Link Posted: 11/15/2003 11:15:56 PM EDT
Just going on what I heard years ago. You know how it is, you hear something, but can't recall where it was, but it sticks with you. I'm glad to hear that my previous belief was incorrect. Cool. Now I can get a 1/7 with no worries. :) Thanks for the info, guys.
Link Posted: 11/16/2003 4:30:32 PM EDT
stuh505, well put! I'm building up a supply of q3131a for my 1/7 and I feel just all the more better now. It's a heck of a lot cheaper than the heavy stuff. Plus, in 5.56 chamber, I'm hoping it may help accuracy.
Link Posted: 11/17/2003 2:02:26 AM EDT
[Last Edit: 11/17/2003 2:03:14 AM EDT by DevL]
SS109 fragemnts more than M193 going through multiple intermediate barriers and would actually be a better choice if you were concerned with over penetration in a house. Its a poor barrier solution when you want terminal effects on the other side of the barrier. No though was given to the terminal effects of M855 or the SS109 bullet. You have jacket and penetrator seperation after passing through barriers and end with with very little weight making its way to the target. If you want penetration get a Trophy Bonded Bear Claw.
Link Posted: 11/18/2003 6:10:41 AM EDT
My 1/7 ROCKS! Its a 20" and I shoot M193-Q3131A. Must say it is very accurate, and a 16" 1/7 is on my wish list.
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