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PostPosted: Fri Dec 01, 2017 4:24 pm 
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Joined: Fri Aug 26, 2016 9:50 am
Posts: 114
Location: Nova Scotia
Can anyone explain exactly what needs to be done to fit a backpacker pump arm onto the new style P1322? I know it will need to be countersunk drilled...but is that all...and if so, to what depth?

thx in advance

Sent from my B1-770 using Tapatalk


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PostPosted: Fri Dec 01, 2017 6:55 pm 
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Joined: Thu May 07, 2015 8:30 pm
Posts: 1184
Location: Eastern Townships
My advice would be to buy new screws, they are the commoly available size 6-32NC, 1 1/2'' in length for the rear hole and 1 1/4'' for the front hole (you could trim the length to your taste if necessary). You then countersink just enough so the heads are flush with the forearm surface (about 1/8'' deep), as on your current forearm. The roll pins holes in the 2289 forearm seem to be a tiny bit tighter than on the new style 13xx forearm, which is not a bad thing, it'll give you good support.

If you want to use the original screw, you will need to countersunk very deep, about 1/2'' for the rear hole and 5/16'' for the front one. The problem I see is that the ''crossmember'' (indicated by red arrows on the picture) on the 2289 forearm in thinner (0.268'') than the one on the 13xx forearm (0.310), and if you countersink deep enough to give a good support to the screws on both sides, you will weaken that area. The screws ''pocket'' are 0.284'' in diameter, already larger than the thickness of the 2289 forearm crossmembers. Also you can see in the second picture that the 13xx screws are shorter than the inside width of the 2289 forearm, not much material left to support the effort of pumping IMO.

I hope that it'll help, and that it makes some sense, I'm not always good at explaining things in English :oops:


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13xx_forearms.JPG
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PostPosted: Sat Dec 02, 2017 6:48 pm 
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Joined: Fri Aug 26, 2016 9:50 am
Posts: 114
Location: Nova Scotia
airmec wrote:
My advice would be to buy new screws, they are the commoly available size 6-32NC, 1 1/2'' in length for the rear hole and 1 1/4'' for the front hole (you could trim the length to your taste if necessary). You then countersink just enough so the heads are flush with the forearm surface (about 1/8'' deep), as on your current forearm. The roll pins holes in the 2289 forearm seem to be a tiny bit tighter than on the new style 13xx forearm, which is not a bad thing, it'll give you good support.

If you want to use the original screw, you will need to countersunk very deep, about 1/2'' for the rear hole and 5/16'' for the front one. The problem I see is that the ''crossmember'' (indicated by red arrows on the picture) on the 2289 forearm in thinner (0.268'') than the one on the 13xx forearm (0.310), and if you countersink deep enough to give a good support to the screws on both sides, you will weaken that area. The screws ''pocket'' are 0.284'' in diameter, already larger than the thickness of the 2289 forearm crossmembers. Also you can see in the second picture that the 13xx screws are shorter than the inside width of the 2289 forearm, not much material left to support the effort of pumping IMO.

I hope that it'll help, and that it makes some sense, I'm not always good at explaining things in English :oops:
That was incredibly helpful and easy to understand...thanks for helping :)

Sent from my B1-770 using Tapatalk


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PostPosted: Sat Dec 02, 2017 8:03 pm 
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Joined: Wed Jul 26, 2017 7:01 pm
Posts: 2102
Location: GTA, ON
To my own experience, just put your hands on and it's not that complicated as it looks~ (especially you already got such a good guide line here ~ [emoji16][emoji16])

I replaced the forearm for my 1322 too. Before I started, I think about the 2289 forearm first, but it looks complicated... so finally I bought a solid wood piece forearm which said it's just the replacement for the stock forearm...

To my surprise, it also comes with two straight hex screw without the head so you can use them to replace the stock screws and buried them completely into the wood piece...

Everything looks prefect and piece of a cake , right ?

Alright, the truth I found after putting my hands on this project is another story at all...

First ...the new screws are useless... because of its size, the hex head is not big enough to bear the force from the driver to screw it through the wood piece to the other side (with pre-drilled hole already), the hex driver destroyed the head in half way...both screws same...

Second, I used the stock screws then and found the screws are too short because the wood forearm is thicker than the stock plastic piece... and the screw head is out of the wood piece. Not good looking but also affect your actions while pumping and holding the gun while aiming...

So , finally I need to use a bigger drill bit to make sink hole for the wood forearm and looks for a longer same thread size screw to replace the stock ones... I remember the one I find was too long (a little too long or not enough long, I have to take the longer one right ?), and need to use a fine to make it to proper size...

I thought I can save some work but actually did all the same plus some other works ~ but it's a good experience after all done~ I know my gun much more then~ [emoji16]

So ,I think you will have a better experience than me as all I got were unexpected and need to stop the job to look for answers again and again~

Sent from my LG mobile

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