This will not be a how-to article. Instead I will examine the cost and performance of a conversion and the reasons to convert. Here we go….

About 10 years ago, I had a job where I worked alone, had 7.5 hrs of down time, and a plethora of European starlings. Enter the 1377. I had a lot of fun there.

Last year I found that 1377 in my parents garage. I found some pellets and went to work…

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I was in love again. The pistol came home with me and I googled “Crosman 1377.” I was amazed with all the modifications available for the pistol. I didn’t own a sweet air rifle, but I was about to make one.

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With the addition of a 1399 stock and a 2-7x 20 Tasco the carbine became a tack driver under 30 yards. As I started pricing parts, I abandoned the project for about a year. After I completed the Crosman 2400 .177 pcp conversion I realized I had most parts needed for the conversion.

My goal for the conversion was to make a .22 carbine that had about 10fpe and was accurate to 25 yards.

Parts used/cost
Crosman 1377 ($50)
.22 steel breech and 18″bbl ($50)
1389 forearm and 1399 stock ($50)
Flat top piston/valve ($50)
     Alchemy Airwerks
Williams Diopter peep sight  ($30)

Total about $230

Performance

I shot the rifle over the chronograph with Crosman Premier Hollow Point 14.3gr. Shot# equals pump #

Shots
#     FPS        FT-LBS     PF
20    585        10.87      8.37     
19    555        9.78       7.94     
18    568        10.25      8.12     
17    536        9.12       7.66     
16    553        9.71       7.91     
15    553        9.71       7.91     
14    534        9.06       7.64     
13    528        8.85       7.55     
12    511        8.29       7.31     
11    510        8.26       7.29     
10    482        7.38       6.89     
9     474        7.14       6.78     
8     479        7.29       6.85     
7     456        6.60       6.52     
6     432        5.93       6.18     
5     406        5.23       5.81     
4     364        4.21       5.21     
3     330        3.46       4.72     
2     253        2.03       3.62     
1     247        1.94       3.53

At 15 pumps, we come very close to the 10fpe mark. After 15 pumps, gains in velocity are minimal per pump.

Then I shot for consistency. 5 shots 11 pumps:
Shots
#     FPS        FT-LBS     PF
5     492        0.00       0.00     
4     512        0.00       0.00     
3     517        0.00       0.00     
2     496        0.00       0.00     
1     499        0.00 

Everything was going great until I started shooting groups. I tested 10 different pellets at 10 yards with 15 pumps in the rifle. 8 of the 10 grouped about 2″wide. The CPHP’S grouped about  .75″. Then I shot the JSB 18gr:

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Every group was about .5″ that is 3 shots in the photo. Granted it’s only 10 yards, but this is acceptable for my standards in this carbine.

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Here is the competed rifle. I’m pleased with the results. It’s lightweight, rugged, accurate, and has enough power for light duty hunting.

Should you convert?
There are only 2 reasons you should attempt a conversion:

You already have the parts.
Or
You truly enjoy making things.

The cost of the base rifle was about $200 USD. Compare that to a Benjamin 392. The 392 is currently going for around $160 USD. The 392 out of the box has more power and is a time tested hunting rifle. Also, this project was started before Crosman introduced the 1300kt from their custom shop. Just for fun I built a comparable rifle (online) for $169 USD (didn’t include shipping or the flat top valve/piston either) Something for you to ponder.

If you do decide to attempt a Crosman modification beware. This hobby is addicting and gets expensive. I’m currently meditating on building a high powered .25 caliber hunting rifle.

If you have any questions, let me know.

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