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Modified .243 10T issues
12/9/2011 6:49:28 PM
This was a box stock early (2000?) .243 10T with a 24 inch barrel. It ran perfect but was too long and heavy for my tastes. Very accurate, but I f'd with it anyway.
So I had a local guy re profile it and thread the muzzle, turned it .750 at the gas block and it is 18" long now.
I put a factory armalite carbine stock kit on it, their spring and buffer.
All testing (Ha!) was done using the same 100gr. federal softpoints that used to run great.
When I shot it the first few times, it didn't eject and reload itself every time. Most stayed in the gun, so I thought maybe my new lopro gasblock is out of whack, and tried to line it up again. I was on to something there, because the gun gun now runs,,,,, but it is not catching the bolt face with the bolt stop. The bolt face stops right at the back of the feed lips on an inserted mag.
Im thinking about the gas port size and decided to try an H buffer to see what effect that would have. Same performance with the H buffer....I was just sure this would cure it.
Now I'm kinda at a loss here.
So I had a local guy re profile it and thread the muzzle, turned it .750 at the gas block and it is 18" long now.
I put a factory armalite carbine stock kit on it, their spring and buffer.
All testing (Ha!) was done using the same 100gr. federal softpoints that used to run great.
When I shot it the first few times, it didn't eject and reload itself every time. Most stayed in the gun, so I thought maybe my new lopro gasblock is out of whack, and tried to line it up again. I was on to something there, because the gun gun now runs,,,,, but it is not catching the bolt face with the bolt stop. The bolt face stops right at the back of the feed lips on an inserted mag.
Im thinking about the gas port size and decided to try an H buffer to see what effect that would have. Same performance with the H buffer....I was just sure this would cure it.
Now I'm kinda at a loss here.
12/9/2011 7:34:21 PM
Sounds as though your gonna have to open up your gas port. What kinda loads were you running? Didja use more than one type?
12/9/2011 7:37:47 PM
You cut 6" off the barrel. This drastically reduced dwell time.
You need a bigger gas port.
You need a bigger gas port.
12/9/2011 8:14:36 PM
100 gr federal was the ammo, was hoping there was a workaround besides enlarging the gas port.....
I thought a lighter buffer would do it
now to research gas port sizes,,, and adjustable gas blocks.
Wonder if I should go big on the port, and make the adjustable gas block do the rest...
I thought a lighter buffer would do it
now to research gas port sizes,,, and adjustable gas blocks.
Wonder if I should go big on the port, and make the adjustable gas block do the rest...
12/9/2011 9:22:18 PM
If it were mine I would determine the current size of the gas port and then buy a few drill bits larger than what it is already. By larger bits I mean letter and wire size if required, not in 1/32 or 1/64 increments. Stick a cleaning rod in the bore of the barrel, then proceed with enlarging gas port. Test fire and repeat if necessary.
12/9/2011 10:33:07 PM
Okay, seriously, it's only off by a few thousandths. This is reamer work, not drill bits.
Find a machinist or smith who has a gauge pin set and pin the port. Then order a reamer from MSC the appropriate size larger.
The gun is within .005 of working, I'll just about guarantee it.
Find a machinist or smith who has a gauge pin set and pin the port. Then order a reamer from MSC the appropriate size larger.
The gun is within .005 of working, I'll just about guarantee it.
12/10/2011 7:59:38 AM
Originally Posted By ziarifleman:
Okay, seriously, it's only off by a few thousandths. This is reamer work, not drill bits.
Find a machinist or smith who has a gauge pin set and pin the port. Then order a reamer from MSC the appropriate size larger.
The gun is within .005 of working, I'll just about guarantee it.
Okay, seriously, it's only off by a few thousandths. This is reamer work, not drill bits.
Find a machinist or smith who has a gauge pin set and pin the port. Then order a reamer from MSC the appropriate size larger.
The gun is within .005 of working, I'll just about guarantee it.
There is only a .001 difference in most bits when you go to the wire/letter bits.
Drill Bit Sizes Conversions Number and Letter Drills Fractional Drills Decimal Equivalents
80 ... .0135
79 ... .0145
1/64 .0156
78 ... .0160
77 ... .0180
76 ... .0200
75 ... .0210
74 ... .0225
73 ... .0240
72 ... .0250
71 ... .0260
70 ... .0280
69 ... .0292
68 ... .0310
1/32 .0312
67 ... .0320
66 ... .0330
65 ... .0350
64 ... .0360
63 ... .0370
62 ... .0380
61 ... .0390
60 ... .0400
59 ... .0410
58 ... .0420
57 ... .0430
56 ... .0465
3/64 .0469
55 ... .0520
54 ... .0550
53 ... .0595
1/16 .0625
52 ... .0635
51 ... .0670
50 ... .0700
49 ... .0730
48 ... .0760
5/64 .0781
47 ... .0785
46 ... .0810
45 ... .0820
44 ... .0860
43 ... .0890
42 ... .0935
3/32 .0937
41 ... .0960
40 ... .0980
39 ... .0995
38 ... .1015
37 ... .1040
36 ... .1065
7/64 .1094
35 ... .1100
34 ... .1110
33 ... .1130
32 ... .1160
31 ... .1200
1/8 .1250
30 ... .1285
29 ... .1360
28 ... .1405
9/64 .1406
27 ... .1440
26 ... .1470
25 ... .1495
24 ... .1520
23 ... .1540
5/32 .1562
22 ... .1570
21 ... .1590
20 ... .1610
19 ... .1660
18 ... .1695
11/64 .1719
17 ... .1720
16 ... .1770
15 ... .1800
14 ... .1820
13 ... .1850
3/16 .1875
12 ... .1890
11 ... .1910
10 ... .1935
9 ... .1960
8 ... .1990
7 ... .2010
13/64 .2031
6 ... .2040
5 ... .2055
4 ... .2090
3 ... .2130
7/32 .2187
2 ... .2210
1 ... .2280
A ... .2340
15/64 .2344
B ... .2380
C ... .2420
D ... .2460
E 1/4 .2500
F ... .2570
G ... .2610
17/64 .2656
H ... .2660
I ... .2720
J ... .2770
K ... .2810
9/32 .2812
L ... .2900
M ... .2950
19/64 .2969
N ... .3020
5/16 .3125
O ... .3160
P ... .3230
21/64 .3281
Q ... .3320
R ... .3390
11/32 .3437
S ... .3480
T ... .3580
23/64 .3594
U ... .3680
3/8 .3750
V ... .3770
W ... .3860
25/64 .3906
X ... .3970
Y ... .4040
13/32 .4062
Z ... .4130
27/64 .4219
7/16 .4375
29/64 .4531
15/32 .4687
31/64 .4844
1/2 .5000
33/64 .5156
17/32 .5312
35/64 .5469
9/16 .5625
37/64 .5781
19/32 .5937
39/64 .6094
5/8 .6250
41/64 .6406
21/32 .6562
43/64 .6719
11/16 .6875
45/64 .7031
23/32 .7187
47/64 .7344
3/4 .7500
49/64 .7656
25/32 .7812
51/64 .7969
13/16 .8125
53/64 .8281
27/32 .8437
55/64 .8594
7/8 .8750
57/64 .8906
29/32 .9062
59/64 .9219
15/16 .9375
61/64 .9531
31/32 .9687
63/64 .9844
1 1.0000
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12/10/2011 2:08:04 PM
I know drills come in the same sizes as reamers.
This is still work for a reamer, not a drill.
This is still work for a reamer, not a drill.
12/10/2011 3:40:06 PM
Originally Posted By ziarifleman:
I know drills come in the same sizes as reamers.
This is still work for a reamer, not a drill.
I know drills come in the same sizes as reamers.
This is still work for a reamer, not a drill.
Unless you are going to use a knee mill or someother type of machine tool that you can postively indicate and clamp the barrel into it there would be no benefit. Using a reamer or drill bit will basically give you the same results if using a hand held drill, a hole that is slightly larger and less concentric.
I am not 100% postive but I bet whenever they manufactered the barrel it was not reamed at the gas port. But I bet it was in some type of fixture to keep the GP hole 90 degres to the bore all while using a drill bit.
12/10/2011 3:49:08 PM
Here's what I've got for a port size. The tightest drill to fit mikes at ................................. .061" 
No wonder its' hinky.
My next smallest drill size is .077", and it doesn't even begin to fit. So I think I'm going with that for now. Waiting on some replies on this before I make it bigger, thanks for the help.
Oh, and from carbon marks, I got the gas block centered by the blow thru method pretty good.
No wonder its' hinky.
My next smallest drill size is .077", and it doesn't even begin to fit. So I think I'm going with that for now. Waiting on some replies on this before I make it bigger, thanks for the help.
Oh, and from carbon marks, I got the gas block centered by the blow thru method pretty good.
12/10/2011 4:31:20 PM
Originally Posted By KY13FOX:
Unless you are going to use a knee mill or someother type of machine tool that you can postively indicate and clamp the barrel into it there would be no benefit. Using a reamer or drill bit will basically give you the same results if using a hand held drill, a hole that is slightly larger and less concentric.
I am not 100% postive but I bet whenever they manufactered the barrel it was not reamed at the gas port. But I bet it was in some type of fixture to keep the GP hole 90 degres to the bore all while using a drill bit.
Originally Posted By ziarifleman:
I know drills come in the same sizes as reamers.
This is still work for a reamer, not a drill.
I know drills come in the same sizes as reamers.
This is still work for a reamer, not a drill.
Unless you are going to use a knee mill or someother type of machine tool that you can postively indicate and clamp the barrel into it there would be no benefit. Using a reamer or drill bit will basically give you the same results if using a hand held drill, a hole that is slightly larger and less concentric.
I am not 100% postive but I bet whenever they manufactered the barrel it was not reamed at the gas port. But I bet it was in some type of fixture to keep the GP hole 90 degres to the bore all while using a drill bit.
See, I was talking about doing this the right way, not WECSOGing it like Red Jacket Firearms or similar hammer mechanics.
12/10/2011 6:08:03 PM
As for opening up the GP just use a stardard hand drill. As I originally stated put a cleaning rod inside the bore to keep the drill bit from scuffing up your bore. As for the opening I do not know the answer but I would prolly open it up .010 or less at a time.
12/10/2011 6:27:58 PM
It runs, it runs!
Opened the port to .077", runs like a top now. This is the only next size up drill I had, so there you go. Pretty big jump from .061" but it works.
I may pick up an adjustable gas block in the future to see how overgassed it may be, but the rifle works. 37 degrees here when fired, fwiw.
Thanks for the input
Lockstep
Opened the port to .077", runs like a top now. This is the only next size up drill I had, so there you go. Pretty big jump from .061" but it works.
I may pick up an adjustable gas block in the future to see how overgassed it may be, but the rifle works. 37 degrees here when fired, fwiw.
Thanks for the input
Lockstep
12/10/2011 6:44:42 PM
Great!
12/10/2011 9:41:48 PM
Your barrel will never know the difference whether you use a drill or a reamer.
12/11/2011 7:00:46 AM
The AMU has a $40k machine that is used only to cut gas holes they are fanatical about blue printing its placement and cutting w/o a burr. I suppose like receiver lapping its all about which voodoo you believe in.
That said since wre talking about a lothar barrel I agree 100% this barrel will never know. Did you scope that barrel to see how big a burr was created? What does the gas hole errosion look like after the cut did you get a copper clob started. Poorly cut gas holes will adversly affect accruacy and shoorte nthe tube's peak performance round count. But again since we're talking about Lothar it doesn't really matter since the peak performance round count is so low in my experiemce.
That said since wre talking about a lothar barrel I agree 100% this barrel will never know. Did you scope that barrel to see how big a burr was created? What does the gas hole errosion look like after the cut did you get a copper clob started. Poorly cut gas holes will adversly affect accruacy and shoorte nthe tube's peak performance round count. But again since we're talking about Lothar it doesn't really matter since the peak performance round count is so low in my experiemce.
