Rear take down pin trouble??

[customcutter]

Some parts came in the mail today. So I dug out the Spikes lower (blem) that I bought 5 years ago. They said it had a slight discoloration in the finish. I couldn't see it then and still can't see it.

I tried fitting the new billet upper to the lower and the front lug barely fit into the lower. Closed it up and tried to install the back pin. Went through to the far side of the lower, but no joy. I've squeezed the upper and lower pretty hard and pushed and hard as I can on the rear pin with my thumb.

I shot an e-mail off to the supplier, but won't get an answer before Monday. They will probably say it's the lower, and I don't want $20-30 in postage back and forth. I'm thinking of taking a few thousandths off the shoulder at a 45* angle on the pin. Least expensive part to replace.

Any thoughts before I fire up the lathe or grinder?

thanks,
CC

[cory]

Whose billet upper is it?

[customcutter]

Cross Machine made on a 5 axis CNC mill. I looked for reviews before ordering but didn't find any negative in a quick search.

[NugginFutz]

Some parts came in the mail today. So I dug out the Spikes lower (blem) that I bought 5 years ago. They said it had a slight discoloration in the finish. I couldn't see it then and still can't see it.

I tried fitting the new billet upper to the lower and the front lug barely fit into the lower. Closed it up and tried to install the back pin. Went through to the far side of the lower, but no joy. I've squeezed the upper and lower pretty hard and pushed and hard as I can on the rear pin with my thumb.

I shot an e-mail off to the supplier, but won't get an answer before Monday. They will probably say it's the lower, and I don't want $20-30 in postage back and forth. I'm thinking of taking a few thousandths off the shoulder at a 45* angle on the pin. Least expensive part to replace.

Any thoughts before I fire up the lathe or grinder?

thanks,
CC

Have you considered removing the rear pin and fitting the upper to the lower for an alignment check? Before I cut anything, I'd be certain of how much misalignment was present.

It seems to me that skinnying up the rear pin almost ensures that a different upper would have fit issues. I've heard of a few folks that have reamed out the rear hole on their uppers to achieve a fit, but I cringe to think of it.

[customcutter]

Have you considered removing the rear pin and fitting the upper to the lower for an alignment check? Before I cut anything, I'd be certain of how much misalignment was present.

It seems to me that skinnying up the rear pin almost ensures that a different upper would have fit issues. I've heard of a few folks that have reamed out the rear hole on their uppers to achieve a fit, but I cringe to think of it.

The lower isn't assembled to the stock so it's no problem pulling the rear pin and checking alignment. Visually I can't see any mis-alignment, but there is something there not lined up. I would never ream, file, sand, etc the upper or lower. I was going to grind a very small taper on the leading edge of the rear pin to see if that would allow the pin to start into the hole. As I said that's the cheapest part and easily replaced.

[LRRPF52]

Measure the takedown pin OD. It should be .249". If it's .250", it tends to be pretty tight. If you have another TD pin, you can try that one. If not, there isn't anything wrong with putting more of a radius on the tip of the pin that is not wanting to go through the far side of the lower.

You can Oxyblue it once you have removed a little material and polished it, so it doesn't look like garbage. Sounds like you will have a nicely-fit set, provided the mag catch height is correct for your upper.

Your thinking behind modifying the $1 part makes perfect sense to me, rather than messing with the parts that are in the hundreds of duckets. Looking forward to hearing how it turns out.

[customcutter]

Measure the takedown pin OD. It should be .249". If it's .250", it tends to be pretty tight. If you have another TD pin, you can try that one. If not, there isn't anything wrong with putting more of a radius on the tip of the pin that is not wanting to go through the far side of the lower.

You can Oxyblue it once you have removed a little material and polished it, so it doesn't look like garbage. Sounds like you will have a nicely-fit set, provided the mag catch height is correct for your upper.

Your thinking behind modifying the $1 part makes perfect sense to me, rather than messing with the parts that are in the hundreds of duckets. Looking forward to hearing how it turns out.

Just pulled my Remington R-15 out of the safe. The CMT upper fits easily with the Rem lower. Also the Spikes lower fits easily with the Rem upper and the new RTP. I just measured the new RTP with a set of cheap calipers. It measured from .2475-.2485 on three measurements. I think I'm going to grind a very small shoulder on the pin and try it.

thanks for the replies,
CC

[LRRPF52]

Are you saying the ID of the Takedown Pin hole on the billet lower is .2475" - .2485"?

[customcutter]

Are you saying the ID of the Takedown Pin hole on the billet lower is .2475" - .2485"?

No, the OD of the take down pin is .2475" to .2485".

I grabbed a small 6oz brass hammer from the garage and squeezed the upper and lower tightly together, and a couple of very light taps and the pin is going in without modification. I guess I'll be using a plastic mallet and drift pin for assembly/disassembly, till things wear in a little.

[NugginFutz]

Glad to hear it. Your issue is preferable to the alternative, in my opinion. I have one pair that mate with loose tolerances. I'm likely going to install an accuwedge to take out the slop. Yuck.

[ricsmall]

I have a wilson combat upper that fits the same way to an aero precision lower. Id keep it that way rather than grinding the takedown hole.

Richard

[LRRPF52]

I have at least one gun with fit like that, where a brass hammer and delrin punch are needed for in, then out. Doesn't bother me on an accuracy gun that I'm not carrying in the field on continuous ops, and even then, Brownell's has this cool little tool that you can put inside the grip or on a key chain.

[customcutter]

Yes, I'm comfortable at this stage with a hunting rig with the take down being tight. If it were a defense weapon, I would definitely address the problem. I also think from what I read on other forums that it will loosen up slightly as it is shot and wears in.

Edit:

I'm hoping that the barrel extension fit is this tight. :-) One of the few areas that I've heard that "can" affect accuracy.

[jurassic]

Yes, I'm comfortable at this stage with a hunting rig with the take down being tight. If it were a defense weapon, I would definitely address the problem. I also think from what I read on other forums that it will loosen up slightly as it is shot and wears in.

Edit:

I'm hoping that the barrel extension fit is this tight. :-) One of the few areas that I've heard that "can" affect accuracy.

Many are not, that's why a lot of people bed the barrel in the upper using green or blue loctite, I forgot which flavor though.

[NugginFutz]

[/COLOR]

Many are not, that's why a lot of people bed the barrel in the upper using green or blue loctite, I forgot which flavor though.

I have one that I bedded with loctite blue.

[Tedward]

I have the same issue with some Spikes blem lowers, that's why there blems, but for the price they are great. I didn't find one imperfection but the anodizing is a little thick in places so maybe that was why they were less expensive. After 20 times of the pin going in and out an using it, the pin moves better but very snug. Snug is good, less movement between the two units, people pay more for match sets to get that tight fit.

Just like a pair of new shoes needs broke in, just squeeze it together and use it for a while, better fit in due time...

good luck!!

[Lead Chucker]

A buddy had one like that this year, pin wouldnt go through the far side. We found the pin was out of spec by a few thousandths. Some 600 grit sandpaper and a few minunts later it fit fine. Like said above alittle tight is better than slop.