AR 15 Bolt Tail

[titsonritz]

Is this thread REALLY happening?

I can start a lube thread if you would like.

[prepare]

Is this thread REALLY happening?

The gauges are for amorers to pinpoint problems in guns with issues.

A efficient bolt tail run in the carrier is .250-.251

What I'm trying to determine is the best course of action for gauging the bolt tail, continue using a micrometer or a set of ring gauges.

[ViniVidivici]

This thread is going to send a bunch of guys into a "tail" spin.... measuring every bolt in their collection.

Well.....no tail spin, but it's funny, just spotted the thread, got up and measured 3 spare bolts in the parts kit.....just academically curious.

Then saw your post and laughed out loud. HA!

In all these years of getting to know M16 and AR15s, I honestly had no idea this was such an important dimension. Learn something new every day.

Makes sense though. Between it and the gas rings, it comprises the other "end" of that little chamber in back of the carrier. Cool stuff.

[HKGuns]

If you gauge the tail, do you gauge the carrier?

Yep.

[prepare]

Yep.

You've been to SOTAR too I take it?

[HKGuns]

You've been to SOTAR too I take it?

Nope, but I have watched all his videos.

I’d like to attend at some point but they fill up quickly.

I really enjoy learning new things and his videos are fascinating to me.

[prepare]

Nope, but I have watched all his videos.

I’d like to attend at some point but they fill up quickly.

I really enjoy learning new things and his videos are fascinating to me.

This years classes filled up within a few hours of announcing.

I learned a lot even though I've been working on the AR's for awhile part time. If people knew enough to buy quality and not be lured into the latest so called up grades there would not be near as many problems.

[prepare]

Here is just a sample of bolts I have gauged;
BT is Bolt Tail & PT is Protrusion
There are more but I was unable to determine who made the bolt.

1. SOLGW- BT .2499 PT .031
2. BCM- BT .2500 PT .031
3. BCM- BT .2494 PT .034
4. BCM- BT .2494 PT .032 bad gas rings
5. DD- BT .2498 PT .037
6. DD- BT .2497 PT .029
7. BCM- BT .2500 PT .036
8. BCM- BT .2497 PT .034
9. Colt- BT .2498 PT .034
10. Colt- BT .2501 PT .032
11. TC - BT .2497 PT .034
12. BCM- .2498 PT .029 (.252 BTR)
13. TC- .2489 PT .033
14. SOLGW- BT .2497 PT .032
15. SOLGW- BT .2502 PT .030
16.
17.
18. Colt- BT .2486 PT .032
19. BCM- BT .2497 PT .031
20. BCM- .2498 PT .030 bad gas rings
21. CA- .2496 PT .030
22. TC- .2494 PT .035
23. SOLGW .2498 TP .032
24. PSA - BT .2494 PT .033
25. AP- BT .2497 PT .032
26. AP- BT .2502 PT .032
27. BCM- BT .2501 PT .033
28. Armalite- BT .2501 PT .030
29. Expo- BT .2503 PT .034
30. Expo- BT .2507 PT .030
31. WLA- BT .2501 PT .029
31. TC- BT .2501 PT .036
32. AO- BT .2505 PT .028
33. CMT- BT .2500 PT .031
34. AIM- BT .2501 PT .032
35. PSA- BT .2501 PT .032
36. BRT- BT .2501 PT .030
37. BRT- BT .2503 PT .030
38. DD- BT .2507 PT .031
39. EXPO- BT .2500 PT .030
40. SLGW- BT.2501 PT .030
41. Expo- BT .2505 PT .030

[Disciple]

For a used bolt discard if the diameter measures 0.2497"

Here is just a sample of bolts I have gauged;
BT is Bolt Tail & PT is Protrusion
There are more but I was unable to determine who made the bolt.

3. BCM- BT .2494 PT .034
4. BCM- BT .2494 PT .032 bad gas rings
6. DD- BT .2497 PT .029
8. BCM- BT .2497 PT .034
11. TC - BT .2497 PT .034
14. SOLGW- BT .2497 PT .032
18. Colt- BT .2486 PT .032
19. BCM- BT .2497 PT .031
21. CA- .2496 PT .030
22. TC- .2494 PT .035
24. PSA - BT .2494 PT .033
25. AP- BT .2497 PT .032

That's a lot of fail/retire according to that specification. What should I take from this? How old are these bolts?

[prepare]

Half are new half lightly used.

The most consistent measurement out of all those was the bolt tail run in the carrier. All but two were .251